The first two lines from the
wikipedia article on regular expressions (emphasis mine)
Regular expression
In computing, a
regular expression, also referred to as
regex or
regexp, provides a concise and flexible means for matching strings of text, such as particular characters, words, or patterns of characters. A regular expression is written in a formal language that can be interpreted by a regular expression processor, a program that either serves as a parser generator or examines text and identifies parts that match the provided specification.