Source : WordNet®

infix notation
     n : a notation for forming mathematical expressions using
         parentheses and governed by rules of operator precedence;
         operators are dispersed among the operands

Source : Free On-Line Dictionary of Computing

infix notation
     
         One of the possible orderings of {functions} and
        {operands}: in infix notation the functions are placed between
        their operands, such as "1+2".  Although infix notation is
        limited to binary functions most languages mix infix notation
        with {prefix} or {postfix} notation, as a form of {syntactic
        sugar}.
     
        (1997-01-17)