Informational

This status code is primarily intended to be used with the Link header, letting the user agent start preloading resources while the server prepares a response.

This code indicates that the server has received and is processing the request, but no response is available yet.

This code is sent in response to an Upgrade request header from the client, and indicates the protocol the server is switching to.

This interim response indicates that everything so far is OK and that the client should continue the request, or ignore the response if the request is already finished.

Definition:

In HTTP status codes, 100 Continue is an informational response that indicates that the initial part of a client’s request has been received by the server, and the client can continue with the request or ignore the response if the request is already finished.