What is the definition of a regular expression?

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http://unix.stackexchange.com – I recently got into a friendly argument with Ghoti about what constitutes a regular expression in the comments to my answer to this question. I claimed that the following is a regular expression: `[Rr]eading[Tt]est[Dd]ata` Ghoti disagreed, claiming it is a file glob instead. The glob page on wikipedia claims that (emphasis mine): Globs do not include syntax for the Kleene star which allows multiple repetitions of the preceding part of the expression; thus they are not considered regular expressions, which can describe a larger set of regular languages over any given finite alphabe (HowTos)