Source : Free On-Line Dictionary of Computing

hash function
     
         A {hash coding} {function} which assigns a data
        item distinguished by some "key" into one of a number of
        possible "hash buckets" in a hash table.  The hash function is
        usually combined with another more precise function.
     
        For example a program might take a string of letters and put
        it in one of twenty six lists depending on its first letter.
        Ideally, a hash function should distribute items evenly
        between the buckets to reduce the number of {hash collisions}.
        If, for example, the strings were names beginning with "Mr.",
        "Miss" or "Mrs." then taking the first letter would be a very
        poor hash function because all names would hash the same.
     
        (1997-08-03)