HTTP headers are key-value pairs sent between a client (like a web browser) and a server in an HTTP request or response. They convey metadata about the request or response, such as content type, auth information etc.

Common headers

1. Authorization (Sends the user auth information)
2. Content-Type - Type of information client is sending (json, binary etc)
3. Referer - Which URL is this request coming from

Request headers

The headers the client sends out in the request are known as request headers

Response headers

The headers that the server responds with are known as the response headers.

Fetch API