The language of the proxy industry borrows terms from network engineering, web security and data operations. The phrase "backconnect gateway, sticky session, /24 subnet diversity" on a provider's pricing page is meaningless to anyone who does not know these three fields.
This glossary explains the concepts you will meet most often in plain English. The terms are divided into thematic groups; at the end of each group you will find links to our articles that go deeper into the subject.
Basic Concepts
| Term | Meaning |
|---|---|
| Proxy | The intermediary server that sits between the client and the target server and forwards requests on its own behalf. |
| Forward proxy | The proxy that sits in front of the client and manages the exit. This is what is meant when people say "proxy" in everyday use. |
| Reverse proxy | The proxy that sits in front of the server and receives incoming requests. It handles load balancing and caching. |
| Gateway / endpoint | The single entry address the provider gives you. There can be thousands of exit IPs behind it. |
| Backconnect | The other name for the gateway model: you connect to a single address and the exit IP changes behind it. |
| Exit IP | The IP address the target site sees. It does not have to be the same as the address you connect to. |
| Upstream | The next server to which the proxy forwards its own request; used in chained setups. |
A proxy belongs to all four classes at once: "static, dedicated, HTTP, ISP proxy", for example, is a consistent description.
For the details of this classification, see residential, ISP, datacenter and mobile proxy our articles.
Network and Infrastructure Terms
| Term | Meaning |
|---|---|
| ASN | Autonomous System Number. The identity of the organisation that manages an IP block. It is the first signal sites look at when answering the question "is this IP coming from a data centre?" |
| Subnet | A subdivision of an IP block. In IPv4 a /24 means 256 addresses; in IPv6 a /64 denotes a vast range. |
| Subnet diversity | How many different blocks the IPs in the pool come from. Addresses within the same /24 are prone to being blocked together. |
| CGNAT | The operator sharing a single public IP among a large number of subscribers. Standard on mobile networks. |
| NAT | The translation of private network addresses into a public address. The basic function of home routers. |
| TTL | Time To Live. How long a session or a DNS record stays valid. |
| Jitter | The variability of the latency value from one measurement to the next. High jitter means an unstable connection. |
| Packet loss | The proportion of packets that never reach the target. Above 1% it creates a noticeable slowdown. |
Session and Rotation Terms
Sticky and rotating are not opposites; they are two stages of the same cycle. Saying "sticky 10 minutes" means rotation happens every 10 minutes.
| Term | Meaning |
|---|---|
| Rotating proxy | A setup that changes the exit IP on every request or at set intervals. |
| Sticky session | Keeping the same exit IP for a certain period. Essential for work that requires logging in. |
| Session key | The key that states which session you want; it is usually written into the username. |
| Static proxy | An unchanging IP address assigned exclusively to you. |
| Quarantine | Temporarily taking a problematic IP out of the pool. |
| Rate limit | The limit on the number of requests a target site accepts per unit of time. |
| Concurrency | The number of connections that can be kept open at the same time. |
For the practical counterparts of these concepts, see our rotating vs static comparison and our concurrency article take a look.
Authentication and Security Terms
| Term | Meaning |
|---|---|
| IP whitelist | The method of allowing access only from registered IP addresses. |
| Basic auth | Encoding the username and password with Base64 and sending them in a header. It is not encryption. |
| 407 | Proxy Authentication Required. The proxy is asking for credentials. |
| Elite / anonymous / transparent | The three levels of anonymity, according to how much trace the proxy leaves on the target server. |
| Judge | The test endpoint that echoes back every header it receives; the anonymity level is measured with it. |
| DNS leak | Name resolution requests going outside the proxy and giving away your real location. |
| WebRTC leak | The browser exposing your local/real IP through its real-time communication API. |
| JA3 / TLS fingerprint | Recognising the client library from the order of the fields in the TLS handshake. |
| MITM | Man in the middle. Traffic being read or altered by an interposed party. |
To test the leak concepts hands-on, see DNS leak, WebRTC leak and anonymity test tools.
Protocol Terms
This is why SOCKS5 is more "general purpose" than an HTTP proxy: because it works at a lower layer, it can carry protocols other than HTTP as well.
| Term | Meaning |
|---|---|
| CONNECT | The method of telling an HTTP proxy to "open a raw TCP tunnel to this address". This is how HTTPS traffic is carried. |
| Absolute-URI | The request line containing the full URL in a plain HTTP proxy request: GET http://site/ HTTP/1.1. |
| SOCKS5h | The SOCKS5 variant that asks for DNS resolution to be done on the proxy side. It prevents DNS leaks. |
| UDP ASSOCIATE | The command that lets SOCKS5 carry UDP traffic. |
| SNI | The field in the TLS handshake that states which domain name is being connected to. It is sent unencrypted. |
| Keep-alive | Reusing the same TCP connection for more than one request. |
| PAC file | The small JavaScript file that determines which proxy is used for which address. |
If you are undecided about which protocol to choose, our HTTP vs SOCKS5 comparison with SOCKS4 vs SOCKS5 difference articles will show you the way.
Data Operation Terms
| Term | Meaning |
|---|---|
| Scraping | Extracting data from web pages programmatically. |
| Crawling | Systematic navigation by following links; the discovery stage of scraping. |
| Headless browser | A real browser engine that runs without an interface. Needed for content generated with JavaScript. |
| SERP | Search Engine Results Page — the results page of a search engine. |
| Rank tracking | Regularly monitoring your ranking for particular keywords. |
| Geo-targeting | Selecting the exit IP by country, region or city. |
| Antidetect browser | The special browser that assigns a separate fingerprint and proxy to each profile. |
| Fingerprint | The unique identity derived from browser and device characteristics. |
| Quota / bandwidth | The total data volume you can use within your package. |
Commercial Terms
| Term | Meaning |
|---|---|
| Dedicated | An IP allocated to you alone. You are not affected by anyone else's behaviour. |
| Semi-dedicated | An IP shared with a limited number of users (usually 2–3). |
| Shared | An IP shared with a large number of users. The cheapest and the riskiest. |
| SLA | Service level agreement. Usually expressed as an uptime percentage. |
| Uptime | The percentage of time the service is available. 99.9% means around 43 minutes of downtime a month. |
| Fair use | The written cap policy applied to "unlimited" packages. |
| Trial | A short or volume-limited test before purchase. |
Keep the practical meaning of uptime percentages in mind: 99% means around 7 hours of downtime a month, 99.9% around 43 minutes, and 99.99% around 4 minutes. The difference is small in the numbers and large in operations.
Error and Status Codes
The source of the code is critical: 407 comes from the proxy, 429 from the target, and ECONNRESET can come from either. When debugging, identify the source first.
Summary
This glossary covers most of the concepts you will come across while reading a proxy provider's technical documentation or pricing page. To see the practical counterparts of the terms you can work through our category pages; and if you are wondering which class an address you have actually falls into, with the proxy checker tool you can find out its protocol, its exit IP and its anonymity level in one go.