Pip stands for percentage in point and is the smallest increment of trade in FX. In the FX market, prices are quoted to the fourth decimal point. For example, if a bar of soap in the drugstore was priced at $1.20, in the FX market the same bar of soap would be quoted at 1.2000. The change in that fourth decimal point is called 1 pip and is typically equal to 1/100th of 1%.
Among the major currencies, the only exception to that rule is the Japanese yen. One dollar is worth approximately 100 Japanese yen; so, in the USD/JPY pair, the quotation is only taken out to two decimal points (i.e., to 1/100th of yen, as opposed to 1/1000th with other major currencies).