Difference between Pin (Punya) and Kusal(Kushala)?

I have seen people using the words *Pin* ("good deeds") interchangeably with *Kusal*; and *Paw* ("bad deeds") interchangeably with *Akusal*. But there are clear differences between them -- per my understanding: * *Pin* (Good deeds) - Actions done physically, verbally or with mind that has good karmas * *Kusal* - Anything that would lead you in the path to nirvana. (*Paw* (Bad deeds) and *Akusal* are the opposites of the above.) But I'm not sure about these definitions. I would like to know the exact meaning of these and how they are related to each other?