Source : Free On-Line Dictionary of Computing

pattern matching
     
        1. A function is defined to take arguments of a particular
        type, form or value.  When applying the function to its actual
        arguments it is necessary to match the type, form or value of
        the actual arguments against the formal arguments in some
        definition.  For example, the function
     
        	length []     = 0
        	length (x:xs) = 1 + length xs
     
        uses pattern matching in its argument to distinguish a null
        list from a non-null one.
     
        There are well known {algorithm} for translating pattern
        matching into conditional expressions such as "if" or "case".
        E.g. the above function could be transformed to
     
        	length l = case l of
        		   []   -> 0
        		   x:xs -> 1 : length xs
     
        Pattern matching is usually performed in textual order though
        there are languages which match more specific patterns before
        less specific ones.
     
        2. Descriptive of a type of language or utility such as {awk}
        or {Perl} which is suited to searching for strings or patterns
        in input data, usually using some kind of {regular
        expression}.
     
        (1994-11-28)