Why is “Expires” 1981?

Question

My CRON Job returned an error that CRON job did not work. In that this was there:

Set-Cookie: PHPSESSID=2t2drultihqc         


        

Answer 1

HTTP Expires header

http://www.w3.org/Protocols/rfc2616/rfc2616-sec13.html

It is set to negative or past value, to prevent caching of response.

Quite common usage of this header.