To do an eyeball search is to look for something specific in a mass of code or data with one's own native optical sensors, as opposed to using some sort of pattern matching software like grep or any other automated search tool. Also known as vgrep or ogrep, i.e., "visual/optical grep".

The most important application of eyeball search / vgrep is vdiff.

From the on-line hacker Jargon File, version 4.4.6, 25 Oct 2003