Hi Toqual,
An Act is the actual primary piece of legislation that operates in the area. It is the most common and often the most relevant one to look at.
A Regulation is sort if the 'procedural' set of rules, less commonly referred to.
Not sure what EPIs are, I have never heard the term.
Repealed just refers to the fact that the Act or Regulation is obsolete, no longer operating.
Hope that helps.
Paul.