Define regular. regular synonyms, regular pronunciation, regular translation, English dictionary definition of regular. adj. 1. Customary, usual, or normal: the train's regular schedule.
A regular expression (shortened as regex or regexp), [1] sometimes referred to as a rational expression, [2][3] is a sequence of characters that specifies a match pattern in text. Usually such patterns are used by string-searching algorithms for "find" or "find and replace" operations on strings, or for input validation.