A keep-alive session refers to a method that allow web browsers to persist an HTTP connection between multiple requests. The primary purpose of a keep-alive session is to prevent a connection from being closed after a single request, thus reducing the overhead of repeatedly establishing new connections for each interaction.

In web technology, a keep-alive session is often associated with the HTTP. It is often HTTP keep-alive session, and also often referred to as HTTP persistent connection. Typically, when a web browser makes an HTTP request to a server, a new connection is established for each request. The connection is then closed after the response is received. This approach is inefficient especially when a web page has multiple resources that need to be loaded.

With HTTP keep-alive, the connection between the client (e.g., a web browser) and the server is kept open after the initial request is made. This allows multiple requests and responses to be sent over the same connection without the need to establish a new connection for each one. Keeping the connection alive reduces latency and overhead, as well as improving the speed of loading web pages, which is particularly important for modern web applications.

It should be noted that HTTP/1.1 introduced the "Connection: keep-alive" header as a default behavior, so modern web browsers and web servers typically use keep-alive sessions by default. In HTTP/2, a more efficient protocol, this concept is further enhanced through multiplexing, allowing multiple requests and responses to be interweaved on a single connection.

A Keep-alive session is not limited to HTTP. A similar concepts are used in other network protocols to maintain long-lived connections to reduce connection setup and teardown overhead. These mechanisms are commonly used in real-time communication systems, online gaming, and various network applications.