In Brazil, pieces of legislation are usually referred to by either a number (e.g. lei n° 6.404/76) or a name (e.g. Lei das SA). When translating into English, use Law when mentioning the number (e.g. Law No. 6,404) and Act when mentioning the name (e.g. Corporation Act).
There are multiple definitions - click on the translation that matches your context.
a law, rule or formal decision made by the legislature or other law-makers
The Human Rights Act is not just a normal Act of Parliament that can be repealed or amended at will.
something done by a person for a particular purpose
I don't understand why anyone would want to commit such acts.