Swap (overnight)
The cost or income of holding a position overnight (rollover): the interest-rate difference between currencies on forex, or CFD leverage financing.
Definition
A swap (also called rollover or overnight cost) is the amount charged for holding a position overnight. On forex it follows from the interest-rate difference between the two currencies; on CFDs it is often added as a cost of leverage. The broker presents it in the symbol specification, separately for long and short — that number belongs in your calculation of the cost of holding.
Example
A long position in a pair whose bought currency has the higher interest rate is often charged a negative swap, while the opposite construction can pay a positive swap. Holding through the weekend is sometimes settled as a “triple day”.
Anti-example / common mistake
Assuming that “a day trade pays no swap and a swing trade does not have to count it”. Whenever you hold a position overnight, the swap applies to every night — measure it as a fraction of 1R instead of ignoring it because “it is only retail”.