A pip (short for percentage in point) is the standard unit used to measure price movements in the Forex market. On most Forex pairs, one pip equals the 4th decimal place. For example, if EUR/USD moves from 1.0850 to 1.0851, that's a 1-pip move.
On pairs involving the Japanese yen (USD/JPY, EUR/JPY...), one pip equals the 2nd decimal, because the JPY is quoted with one fewer decimal. If USD/JPY moves from 150.25 to 150.26, that's also 1 pip.
Most brokers also display pipettes — 1/10 of a pip (5th decimal) — for tighter spread quoting. A 0.8-pip spread equals 8 pipettes.
The monetary value of a pip depends on your position size: on 1 standard lot (100,000 units) in EUR/USD, 1 pip equals roughly $10. On a mini-lot (10,000 units), 1 pip equals $1. This value is essential to calculate your risk before each trade.