Forex Swap?

Hi guys, i'm a bit confused with the term swap here.
I'm wondering if anyone can explain what swap means here in forex trading.
When i leave my position overnight, sometimes i got more money by the swap, sometimes i paid for it. Can you explain it to me what is it actually in terms of what happen between the broker, seller and buyer, why does it occur, and the connection to interbank overnight interest rate.

O yeah, is it related to the term swap as a kind of derivative?

Swap IS the overnight interest rate, also called roolover.
However, it is not exactly the same at every brokerage.

You should check directly with your broker to see what are the rates, and google "forex swap rates", there is a lot of information about it