Glossary
Proxy terms, in plain English
One sentence per term up top, the detail underneath, and a link to the guide that goes further. Written by a provider that would rather you understood what you buy.
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- 407 Proxy Authentication Required
- 407 Proxy Authentication Required is the HTTP status a proxy returns when a request reaches it without credentials it accepts.
- 429 Too Many Requests
- 429 Too Many Requests is the HTTP status a server sends when a client exceeds its rate limit, often with a Retry-After header saying when to try again.
A
- Anonymous proxy
- An anonymous proxy hides your IP address from the website but still reveals, through headers such as Via, that a proxy is in use.
- Antidetect browser
- An antidetect browser runs many isolated profiles, each with its own fingerprint, cookies and proxy, so separate accounts do not look linked.
- ASN
- An ASN (autonomous system number) identifies a network that routes its own IP ranges on the internet, such as an ISP, a cloud host or a university.
B
- Backconnect proxy
- A backconnect proxy is one gateway address that forwards each connection out through an IP drawn from a pool, so the exit can change with no new settings.
- Bandwidth billing
- Bandwidth billing is pricing a proxy by the gigabytes of traffic you send and receive through it, rather than by the number of IPs or requests.
- Bot detection
- Bot detection is the set of checks a website runs to tell automated clients from people, from IP reputation to TLS fingerprints to behaviour.
- Browser fingerprint
- A browser fingerprint is the mix of browser and device traits, such as screen, fonts, canvas output and timezone, that lets a site recognise a visitor.
C
- CAPTCHA
- A CAPTCHA is a challenge a website shows to tell people from bots, such as picking images, ticking a box or passing an invisible browser check.
- CIDR notation
- CIDR notation writes an IP range as an address plus a prefix length, such as 203.0.113.0/24, where the prefix says how many leading bits are fixed.
- Concurrency
- Concurrency is how many requests or connections a client keeps open at the same moment, whether through one proxy IP or across a whole pool.
D
- Datacenter proxy
- A datacenter proxy uses an IP address owned by a hosting or cloud provider rather than a consumer ISP, making it fast and cheap but easy to identify.
- Dedicated proxy
- A dedicated proxy is an IP address assigned to one customer only, so nobody else's traffic shapes its reputation or uses up its rate limits.
- DNS leak
- A DNS leak is when your device looks up hostnames through your own network's resolver while the traffic itself goes through a proxy or VPN.
E
- Elite proxy
- An elite proxy forwards requests without adding any header that reveals your IP or the proxy itself, which is why it is also called a high-anonymity proxy.
- Exit node
- An exit node is the machine whose IP address a website sees at the end of a proxy route, as opposed to the gateway your client first connects to.
F
- Forward proxy
- A forward proxy is a server that sends requests to the internet on behalf of its clients, so websites see the proxy's IP instead of the client's.
G
- Geo-blocking
- Geo-blocking is a website restricting or changing its content based on the country or region that a geolocation database assigns to your IP address.
- Geo-targeting
- Geo-targeting is choosing the country, region or city of the proxy IP your requests exit from, so a site serves you its local content.
H
- Headless browser
- A headless browser is a real browser engine running without a visible window, driven by code to load pages, run JavaScript and extract content.
- HTTP CONNECT
- HTTP CONNECT is the request a client sends to a proxy to open a raw TCP tunnel to a host, which is how HTTPS traffic passes through an HTTP proxy.
- HTTP proxy
- An HTTP proxy speaks HTTP to your client, forwarding plain HTTP requests itself and tunnelling HTTPS traffic through the CONNECT method.
- HTTP/2 fingerprint
- An HTTP/2 fingerprint identifies a client from the settings, flow-control values, priorities and header order it sends when an HTTP/2 connection opens.
- HTTPS proxy
- HTTPS proxy means either an HTTP proxy used to reach HTTPS sites through a CONNECT tunnel, or a proxy you connect to over TLS; the two are often confused.
I
- IP allowlist
- An IP allowlist is a list of your public IP addresses that a proxy accepts connections from without asking for a username and password.
- IP reputation
- IP reputation is the trust score that websites and security vendors give an IP address, based on its network type, history of abuse and recent behaviour.
- IP rotation
- IP rotation is the practice of changing the IP address your requests come from, per request, per session or on a timer, to spread load across addresses.
- IPv6 proxy
- An IPv6 proxy exits from an IPv6 address: cheap and plentiful, but it only works on websites that accept IPv6 connections.
- ISP proxy
- An ISP proxy is a static IP registered to a consumer internet provider but hosted on server hardware, pairing a residential-looking owner with datacenter speed.
J
- JA3
- JA3 is a TLS client fingerprint that hashes the version, ciphers, extensions, curves and point formats of a ClientHello into a 32-character MD5 string.
- JA4
- JA4 is a TLS client fingerprint from FoxIO that sorts ciphers and extensions before hashing, so it gives a readable string that stays stable across connections.
L
- Latency
- Latency is the time a request spends waiting on the network, and through a proxy it includes the extra legs from you to the proxy and on to the site.
M
- Man-in-the-middle
- A man-in-the-middle is a party placed between a client and a server that can read or alter their traffic, a position every proxy occupies by design.
- Mobile proxy
- A mobile proxy exits through a cellular carrier's network, so websites see an IP address that is shared by many phones on 4G or 5G.
N
- NO_PROXY
- NO_PROXY is an environment variable listing hosts and domains that HTTP clients should reach directly, bypassing the proxy set in HTTP_PROXY and HTTPS_PROXY.
O
- Open proxy
- An open proxy accepts connections from anyone on the internet with no authentication, usually through misconfiguration and sometimes as a trap.
P
- PAC file
- A PAC file is a proxy auto-config script: a JavaScript function that tells a browser which proxy to use, or none, for each URL it requests.
- Pay as you go
- Pay as you go is buying proxy traffic or IPs in the amounts you need, when you need them, with no monthly plan or commitment to fill.
- Proxy chain
- A proxy chain routes traffic through two or more proxies in sequence, so that each hop only knows the one before it and the one after it.
- Proxy manager
- A proxy manager is software that sits between your tools and your proxies, choosing which proxy each request uses and handling rotation, rules and retries.
- Proxy pool
- A proxy pool is the set of IP addresses your requests can be spread across, either a provider's rotating network or your own list of static proxies.
- Proxy server
- A proxy server is an intermediary that receives your network requests and sends them on to their destination under its own IP address.
- Proxy-Authorization
- Proxy-Authorization is the HTTP request header that carries your proxy username and password to the proxy server, usually as base64-encoded Basic credentials.
R
- Rate limiting
- Rate limiting is a server capping how many requests a client may make in a time window, usually counted per IP, account, session or API key.
- Rate lock
- A rate lock is a provider's promise to keep charging the price you bought at for a set period, even if its list price rises in the meantime.
- Residential proxy
- A residential proxy routes your traffic through an IP address a consumer internet provider assigned to a home connection, usually from a rotating pool.
- Reverse proxy
- A reverse proxy is a server that sits in front of websites and receives requests on their behalf, for load balancing, caching, TLS or bot filtering.
- robots.txt
- robots.txt is a plain-text file at a site's root that tells crawlers which paths they may fetch, standardised as the Robots Exclusion Protocol in RFC 9309.
- Rotating proxy
- A rotating proxy gives your requests a different exit IP from a pool, on every request or new connection, through one unchanging endpoint.
S
- SERP
- A SERP (search engine results page) is the page a search engine returns for a query, with ads, organic results and features such as maps and answers.
- Shared proxy
- A shared proxy is an IP address several customers use at the same time: cheaper than a dedicated one, but its rate limits and reputation are shared.
- SNI
- SNI (Server Name Indication) is the TLS extension in which a client names the website it wants, in clear text, before the encrypted session begins.
- SOCKS5
- SOCKS5 is a proxy protocol that relays raw TCP connections, and optionally UDP, for any application, with optional username and password authentication.
- socks5h
- socks5h is the proxy URL scheme that tells a client to send hostnames to the SOCKS5 proxy for resolution instead of looking them up locally.
- Static IP
- A static IP is an address that stays the same for as long as you hold it, unlike a rotating or dynamic address that changes between sessions.
- Sticky session
- A sticky session asks a rotating proxy pool to keep routing your requests through the same exit IP for a while, instead of changing it each time.
- Success rate
- Success rate is the share of proxy requests that return the content you wanted, and the figure means little until you know how success was defined.
T
- TLS fingerprint
- A TLS fingerprint identifies the software making a connection from details of its TLS ClientHello, such as cipher suites, extensions and their order.
- Traffic expiry
- Traffic expiry is when prepaid proxy gigabytes stop being usable after a set period, often at the end of a billing month, whether or not you used them.
- Transparent proxy
- A transparent proxy is one of two things: a network proxy that intercepts traffic with no client setup, or a proxy that passes your real IP on to websites.
- TTFB
- TTFB (time to first byte) is the time from sending a request until the first byte of the response arrives, covering network, proxy and server delay.
U
- Unmetered bandwidth
- Unmetered bandwidth means a proxy is billed per IP or per period with no charge per gigabyte, though speed and fair-use limits can still apply.
- User-Agent
- User-Agent is the HTTP request header in which a client names its software and version, and one of the first things sites check to spot scripts.
V
- Via header
- Via is an HTTP header that proxies add to show a request or response passed through them, naming the protocol version and a proxy identifier.
W
- Web crawler
- A web crawler is a program that discovers pages by fetching URLs and following the links it finds, building a list of pages to index or scrape.
- Web scraping
- Web scraping is extracting data from web pages with software, by fetching the HTML or rendered page and parsing out the fields you need.
- Web scraping API
- A web scraping API is a service you send a URL to and get the page back from, with proxies, retries and often browser rendering handled on its side.
- WebRTC leak
- A WebRTC leak is when a browser's real-time connection feature reveals your real IP address to a site even though your web traffic uses a proxy.
X
- X-Forwarded-For
- X-Forwarded-For is an HTTP header listing the client IP addresses a request passed through, added by proxies and load balancers along the way.
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