HTTP Status Code 100 refers to Continue. This informational code indicates that the initial part of a request has been received, and the client should proceed with sending the rest if there is more data to transmit. This is especially useful for large request bodies, commonly used with POST or PUT requests.
Typically, a client sends a request header with an Expect: 100-continue header to check if the server is willing to accept the request body. The server then responds with 100 Continue if it is ready to receive the full request. This process prevents the client from sending large data unnecessarily if the server might reject the request. If the server is not prepared to accept the request, it may respond with another status code, such as 417 Expectation Failed, to indicate that the request should not proceed.
100 Continue helps improve efficiency by ensuring the server is prepared to handle the request before the client sends large data.