Regular Expression: (regex or regexp) is a sequence of characters that forms a search pattern,mainly for use in pattern matching with strings,or string matching. (From wiki)

Lists of a particular category of characters,operators and constructs that can be used to define regular expressions:

Character Escapes:

Character Classes: matches any one of a set of characters.

Anchors: cause a match to succeed or fail depending on the current position in the string.

Grouping Constructs

Quantifiers:

Backreference Constructs: allows a prevIoUsly matched subexperession to be identified subsequently in the same regular expression.

Alternation Constructs: Modify a regular expression to enable either/or matching.

Substitutions: are regular expression language elements that are supported in replacement patterns.

Regular Expression Options:

Miscellaneous Constructs:

References:http://msdn.microsoft.com/en-us/library/az24scfc(v=vs.110).aspx