A flood plain is a land area that is subject to periodic flooding, usually as a result of being close to a body of water or being at or below sea level. When describing a flood plain, it is common to refer to how frequently the flooding is expected. When the term "annual flood plain" is used, that means the area is expected to flood once each year. If a flood plain is described as a "100 year flood plain," then that area is only expected to experience flooding once in a century. The Federal Emergency Management Agency defines a flood plain as an area designated to possibly be subject to flooding once 100 years. Flood insurance companies and FEMA base many insurance decisions on flood hazard boundaries and defined flood plains.