what for

The phrase "what for" is used for questioning the purpose of or reason for an action or plan. It is an informal and somewhat old-fashioned expression that is used to ask why someone does something or to ask what purpose or use something has. For example, "Shes decided to work part-time." "What for?". The phrase can also be used to refer to harsh words or punishment, as in "Just wait until he gets home. Ill give him what for". The origin of the phrase is believed to be a very old British idiom that derives from a rhetorical question, "say please", "what for?", "Ill give you What For!".