What is the meaning of Warhorse?

Any horse used in horse-cavalry, but especially one bearing an armoured knight.

An experienced person who has been through many battles, situations or contests; someone who has given long service.

A regularly revived theatrical or musical work, as with Hamlet or a Beethoven symphony, or as excerpts thereto. May imply that the work in question has become hackneyed.

Source: wiktionary.org