Five hundred year flood - an area has a 0.2% chance (1 in 500) of a flood every year.
Flash flood - short term flooding caused by heavy rainfall in a short time period (usually 6 hours or less) or a dam failure.
Flood - longer term flooding over several days due to rainfall over an extended time period, snow melt or ice jams.
Flood watch - issued when flooding is possible, but not imminent or occurring.
Flood warning - issued when flooding is imminent or occurring.
Flash flood warning - issued when flooding is in progress or will occur within 6 hours.
Flood plain - strip of relatively flat and normally dry land alongside a stream, river, or lake that is covered by water during a flood.
Flood of record - highest observed river stage at a given site.
Flood way - the area of the floodplain where water is likely to be the deepest and moving the most quickly. This area should be kept free of obstructions to allow floodwaters to move downstream.
Greenway - a corridor of open space that follows a natural feature such as a stream valley, floodplain.