It stands for geometric average rate option; an Asian option whose payoff depends on the geometric average price of its underlying asset. For example, the payoff of a geometric average rate call can take one of two values: zero or the positive difference between the geometric average of the underlying’s price over the lifetime of the option and the strike price. In other words, the payoff is given by:

Max (A — S, 0)

Where: A the geometric average of the price, S the strike price.