Pip stands for "percentage in point". It is a unit of change in exchange rates. The pip is the fourth digit after the decimal point in the exchange rate, equal to 0.0001.
In this example, with GBP / USD currency pair, the Pip for the Sell price is 20, whereas the Pip for the Buy price is 22.
In transactions involving the Japanese yen, the pip is equal to 0.01, as JPY quotes have just two decimal positions rather than the usual four.
In this example, with the USD and JPY, the Pip for the Sell price is 68, whereas the Pip for the Buy price is 71.