Per Jakob Nielsen “Heuristic evaluation is a discount usability engineering method for quick, cheap, and easy evaluation of a user interface design” (Nielsen, 2005).
It serves as an effective way to find elements of a site which are affecting the overall function of the site with enough structure and support to prove your point.
It starts with a list of “Usability Heuristics”. You can approach this in different ways. There is Nielsen’s list of 10 Usability Heuristics, the severity of which are then graded on a five point scale.
Traditionally, a tester will go through a website observing the various elements of the website that seem off according to the Heuristics, rate their severity, provide support, and finally a screen shot or linked example.
Quick and easy! It’s a great way to “double check” your work when you launch new things.