A truncheon or baton is essentially a club

Club (weapon)

A club is among the simplest of all weapons. A club is essentially a short staff, or stick, usually made of wood, and wielded as a weapon since prehistoric times....

 of less than arm's length made of wood, plastic, or metal. They are carried for less lethal self-defense

Self-defense

Self-defense, self-defence or private defense is a countermeasure that involves defending oneself, one's property or the well-being of another from physical harm. The use of the right of self-defense as a legal justification for the use of force in times of danger is available in many...

 purposes by law-enforcement officers, correctional staff, security-industry employees and (less often) military personnel. Other uses for truncheons and batons include crowd control or the dispersal of belligerent or non-compliant targets.

A truncheon or baton may be used to strike, jab, block, bludgeon and aid in the application of armlocks.