Threatening

Threatening is the term given in scaring an NPC without much brute force, or killing. To threaten an NPC, simply point a gun to his/her head to make him/her raise his/her hands. This is useful in stopping an NPC's actions. However, threatening the Cops and Street Criminals causes them to fight you back.

Vice City
GTA Vice City introduced a more comprehensive way of threatening. These were store robberies, where the protagonist, Tommy Vercetti can point his gun to a store owner, threatening him to steal money. Robberies in this process also increase you Wanted Level.

San Andreas
While GTA San Andreas did not use the Store Robbery feature from Vice City. Threatening had some minor upgrades in the game. The player may "threaten" a gang member to recruit him. This can also be used to command your gang members to target a selected enemy by means of threatening.

Trivia

 * When your back is turned on a Store Robbery in Vice City. The robbery process will be incomplete, and the owner will be more likely to call Cops.