A "postcode search" refers to the act of looking for a specific area or location by using its postal code. It helps identify and locate places within a particular region quickly and easily. Full definition
Unlike free dating websites, a fee is charged for using many of its services which include postcode searches, instant messaging, unlimited anonymous email, multiple photo uploads and video chat. (datingforgirls.net)
Postcode search find men & women looking for an affair or for sex only. (edateadvisor.com)
In addition to a username search and postcode search there's also a reverse search that looks for members who are looking for people that match your description. (comparethedatingmarketplace.com)