Tide: (Oxford) a regular rise and fall in the level of the sea, caused by the pull of the moon and sun; the flow of water that happens as the sea rises and falls
Tide Pools: (Wikipedia) A tide pool or rock pool is a shallow pool of seawater that forms on the rocky intertidal shore. These pools typically range from a few inches to a few feet deep and a few feet across. Many of these pools exist as separate bodies of water only at low tide, as seawater gets trapped when the tide recedes. Tides are caused by the gravitational pull of the sun and moon. A tidal cycle is usually about 25 hours and consists of one or two high tides and two low tides. Tide pool habitats are home to especially adaptable animals, like snails, barnacles, mussels, anemones, urchins, sea stars, crustaceans, seaweed, and small fish. Inhabitants must be able to cope with constantly changing water levels, water temperatures, salinity, and oxygen content. At low tide, there is the risk of predators like seabirds.