http://lotrtcgwiki.com/forums/index.php/topic,345.0.html•Comprehensive Rules 4.0. section 2
action
Nearly everything that occurs during the game is some kind of action. Players perform actions to play cards, use special abilities, move their fellowships, reconcile, and so on.
Every action is either optional or required. An optional action is defined as: an action that uses the word "may," an event, or a special ability. All other actions are required actions.
If two or more required actions are occurring at the same time (for example, more than one "start of turn" action), the Free Peoples player decides in which order they occur.
All required actions responding to a particular trigger are performed before any optional actions. After all such required actions have resolved, players may perform optional actions responding to that same trigger using the action procedure. (See response.)
See also cost, effect, loops.