The Collaborative International Dictionary of English v.0.48:

Pattern matching \Pat"tern match"ing\, n. [See pattern.]
   (Computers)
   A technique in automated data analysis, usually performed on
   a computer, by which a group of characteristic properties of
   an unknown object is compared with the comparable groups of
   characteristics of a set of known objects, to discover the
   idenity or proper classification of the unknown object.

   Note: There are two major types of pattern matching,
         statistical pattern matching and syntactic pattern
         matching. In statistical pattern matching, the
         criteria used to recognize identity or class membership
         vary, but in general some combination of the
         differences in the groups of characteristics of known
         and unknown objects are considered to be a measure of
         the difference ("distance") between them, and the
         closest known object or objects are viewed as
         presenting the most likely identity or class for the
         unknown object. In syntactic pattern matching, a set of
         known patterns, e.g. as in the possible order of parts
         of speech in a language, is defined, and the unknown
         pattern is compared to find that known pattern or
         patterns which matches the unknown exactly. In general,
         statistical pattern matching is used where properties
         of objects with continuous values are being compared,
         and syntactic pattern matching where a complex
         arrangement of at least two different objects may be
         built by application of a set of rules (a "grammar")
         for combining the objects in a specified order.
         Examples of the latter are natural and formal
         languages.
         [PJC]