A pip ('percentage in point') is the standard smallest unit of price movement in forex. For most pairs it is the fourth decimal place — a move from 1.1050 to 1.1051 is one pip.
For pairs quoted against the Japanese yen, a pip is the second decimal place (e.g. 110.05 to 110.06). Many brokers also quote a fractional 'pipette', a tenth of a pip, shown as a fifth decimal.
Pips let traders measure gains, losses and spreads in a consistent way regardless of the currency.