Stamina is the resource spent to perform combat actions. A normal starting actor has a maximum of 3 Stamina and begins combat full unless an explicit effect says otherwise.
The normal Stamina recovery rate is:
1 Stamina per 5 consecutive Idle ticks
The actor must remain Idle for the required ticks. Leaving Idle before the interval completes resets that interval. Stamina cannot recover above its maximum.
A skill can change the recovery rate or permit another state to count as Idle for a specified purpose. For example, Effortless X can allow an actor to recover while Holding action X. It does not make every Holding state count as Idle.