A Picket

1. A stake driven into the ground.
2. (historical) A type of punishment by which an offender had to rest his or her entire body weight on the top of a small stake.
3. A tool in mountaineering that is driven into the snow and used as an anchor or to arrest falls.
4. (military) One of the soldiers or troops placed on a line forward of a position to warn against an enemy advance; or any unit (for example, an aircraft or ship) performing a similar function.
5. (sometimes figuratively) A sentry.
6. A protester positioned outside an office, workplace etc. during a strike (usually in plural); also the protest itself.
7. (card games, uncountable) The card game piquet.