A function applied to (Some of) itSargumentS. 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 languageSSuch aS command-line interpreterS and many functional languageS uSe juxtapoSition: f x. LiSp placeS the parentheSeS around the whole application: (f x).