The term act has different meanings. It means:
1. Process of doing.
2.A statute, decision by legislature or judicial body such as an act of Congress.
3.A record or document of transactions.
4.A main division of a theatrical work.
5. Performance as in a show or circus.
6.To behave. For example, to act like a fool.
7.A pose or pretense.
In the legal context, Act can be a statute or decision by legislature after a bill has been passed. For example, the Act was passed by Congress.