The standard minimum price movement in a currency pair (usually 0.0001; 0.01 for JPY pairs).
A pip (percentage in point) is the unit used to measure price changes in forex. In most pairs it equals 0.0001; in pairs quoted in Japanese yen it equals 0.01.
The money value of a pip depends on your position size and your account currency. In EUR/USD, one standard lot (100,000 units) is worth about 10 USD per pip. Many brokers also show fractional pips (pipettes), one extra decimal.