HTTP Header Field are defined in a IANA Registry Message Headers
HTTP Header Field may be one of the following:
The HTTP Method/HTTP Status Code line and HTTP Header Fields MUST all end with <CR><LF> (that is, a carriage return followed by a line feed). The empty line must consist of only <CR><LF> and no other whitespace.
For example the "Cache-Control" HTTP Header Field is used to specify HTTP Cache Directives for caches along the request/response chain.