The term 'POOL OR WAVE' can be summarized by the crossword solution 'TIDAL'. TIDAL refers to the periodic rise and fall of ocean water due to the gravitational pull of the moon and sun. This phenomenon is also known as the TIDAL cycle, and it affects the size of coastal bodies of water such as bays, estuaries, and harbors. The term 'pool or wave' is an apt description of this phenomenon, as the ocean's waters can appear to be either a pool or a wave depending on the time of day.