Source : Free On-Line Dictionary of Computing

function application
     
        A {function} applied to (some of) its {argument}s.  If it is
        not applied to all its argument then it is a "{partial
        application}".  Application is usually written in the form
        f(x) but some languages such as command-line interpreters and
        many {functional language}s use {juxtaposition}: f x.  {Lisp}
        places the parentheses around the whole application: (f x).