The Freedictionary defines 'act' as:
1. The process of doing or performing something: the act of thinking.
2. Something done or performed; a deed: a charitable act.
3. A product, such as a statute, decree, or enactment, resulting from a decision by a legislative or judicial body: an act of Congress.
4. A formal written record of proceedings or transactions.
5. One of the major divisions of a play or opera.
a. A performance or entertainment usually forming part of a longer presentation: a juggling act; a magic act.
b. The actor or actors presenting such a performance: joined the act in Phoenix.
7. A manifestation of intentional or unintentional insincerity; a pose: put on an act.
Your guess is as good as mine. I've picked 5, 6 and 7.