Quit is an action performed by pressing the appropriate button when available.
This action is an active choice to stop whatever your hominid is doing.
Mechanics
Certain actions allow your hominid to commit to an action and you have to complete the task. Other actions will allow you the choice to stop before continuing. When Quit appears as an action, you are allowed that choice to stop.
Press the appropriate button when available and your hominid will stop whatever the action you were previously doing.