A more thorough explanation:

A foot acre is a unit of measurement used to describe an area of land or the volume and capacity of reservoirs. It is defined as:

• Acre: An area of land measuring 43,560 square feet.
• Foot Acre: A one-foot-deep layer of coal, water, or other material spread over one acre.

For example, if you have a piece of land that measures one acre, it means that the area of that land is 43,560 square feet. On the other hand, if you have a reservoir that is one foot deep and covers an area of one acre, it is called a foot acre.

The foot acre measurement is commonly used to value coal land for tax purposes. It is also used to measure the volume and capacity of reservoirs. For instance, if a reservoir has a capacity of 10 foot acres, it means that it can hold 10 feet of water over an area of one acre.