A response header is an HTTP header that can be used in an HTTP response and that doesn't relate to the content of the message. Response headers, like Age, Location or Server are used to give a more detailed context of the response.
See Also
How to Enable HTTP Strict Transport Security (HSTS) Policy | Cloudways Help CenterHTTP - MethodsCustomize HTTP security response headers with AD FSHTTP - RequestsNot all headers appearing in a response are categorized as response headers by the specification. For example, the Content-Type header is a representation header indicating the original type of data in the body of the response message (prior to the encoding in the Content-Encoding representation header being applied). However, "conversationally" all headers are usually referred to as response headers in a response message.
The following shows a few response and representation headers after a GET request.
http
200 OKAccess-Control-Allow-Origin: *Connection: Keep-AliveContent-Encoding: gzipContent-Type: text/html; charset=utf-8Date: Mon, 18 Jul 2016 16:06:00 GMTEtag: "c561c68d0ba92bbeb8b0f612a9199f722e3a621a"Keep-Alive: timeout=5, max=997Last-Modified: Mon, 18 Jul 2016 02:36:04 GMTServer: ApacheSet-Cookie: mykey=myvalue; expires=Mon, 17-Jul-2017 16:06:00 GMT; Max-Age=31449600; Path=/; secureTransfer-Encoding: chunkedVary: Cookie, Accept-EncodingX-Backend-Server: developer2.webapp.scl3.mozilla.comX-Cache-Info: not cacheable; meta data too largeX-kuma-revision: 1085259x-frame-options: DENY