grep is the name of a common utility on many Unix or unix like systems.
Folklore says that the name represents a command that developers in the old days used to issue within their editor or other similar program:
g/re/p
which was a global {regular expression} print command.
Grep reads through one or more input streams (stdin or files), searching for a string of text which represents some for of a regular expression, and, depending on options provided, may produce the matching lines of input.