Definitions of poster:

• noun:   a sign posted in a public place as an advertisement

  Example: "A poster advertised the coming attractions"

• noun:   a horse kept at an inn or post house for use by mail carriers or for rent to travelers
• noun:   someone who pastes up bills or placards on walls or billboards
• name:  A surname (very rare: popularity rank in the U.S.: #27245)