*** VERY IMPORTANT***
Basic Flood definition:
A Flood is water covering 2 or more properties, water coming from outside in.
FEMA's definition of a FLOOD:
A general and temporary condition of partial or complete inundation of normally dry land areas from:
(1) The overflow of inland or tidal waters;
(2) The unusual and rapid accumulation or runoff of surface waters from any source;
(3) Mudslides (i.e., mudflows) which are proximately caused by flooding and are akin to a river of liquid and flowing mud on the surfaces of normally dry land areas, as when earth is carried by a current of water and deposited along the path of the current.
A flood inundates a floodplain. Most floods fall into three major categories: riverine flooding, coastal flooding, and shallow flooding. Alluvial fan flooding is another type of flooding more common in the mountainous western states.
Reference FEMA website for more detailed info.