A more thorough explanation:

An acre-foot is a unit of measurement used in irrigation. It measures the amount of water that can cover one acre of land in one foot of water. This is equal to 325,850 gallons of water.

For example, if a farmer has an acre of land and wants to water it with one foot of water, they would need one acre-foot of water, which is equivalent to 325,850 gallons. This measurement is important in agriculture because it helps farmers determine how much water they need to irrigate their crops.