Well "grep" is a program not a shell command or the like here, it's initially developed by Ken Thompson for AT&T UNIX. The term "grep" stands for... global/regular expression/print  [g/re/p] (see the Gnu grep manual, 4 Usage -> QA point 16. for reference ) or global search for a regular expression and print out matched lines ...and stems from the old Unix ed line based texteditor (similar to ex and edlin). Regular expressions have been and are widely used