To stand or march in a public place to protest or demonstrate against something, often with signs or placards. The workers decided to picket the factory to demand better wages.
To act as a picket, or to station pickets, especially to guard or control access to a place during a strike. Union members picketed the entrance to prevent non-union workers from entering.
To tether or secure (an animal, especially a horse) to a stake or rope. The cavalry troops picketed their horses for the night.