Swap is the interest to be charged or given to you if you have a position to stay.
Examples swap calculation is as follows: (please note that the interest rate used is the interest rate for example in 2005′s):
Euro interest rate was 4.25%, and the USA was 3.5%. You have 1 lot EUR/USD Sell position, meaning you sell 100,000 Euros, which means you borrow 100,000 Euros with interest 4.25% / year, and buy dollar where you earn interest of 3.5% / year. Then you will pay (4.25% -3.5%) or about 0.9 points EUR/USD. The sum will produce 675 dollars / year, or about 1.85 dollars per day. Now 1.85 USD per night depending on the broker-will-be inflated in such a way that there is never the same positive swap, let alone greater than the negative swap 1 pair in the same broker.
For example, swap for long at broker A pip is +1.23, then it to sell more than a definite minus 1.23.
Swap from Friday to Monday (2 nights) are usually combined as Wednesday -> Thursday. In most brokers, it will swap multiplied by 3.
Currency rate differences large enough to cause a major swap. For example buy AUD/USD will get a sizable swap, because interest rates are much higher than the AUD/USD. Similarly, the AUD/JPY. Noteworthy is that if you open a sell position AUD/JPY or AUD/USD to days (90% for floating loss), swap sometimes feel too big.