Anything tidal is related to the regular rise and fall of the sea level due to gravitational forces. A marine biologist might study the effects of tidal patterns on local sea life.
Tidal conditions are caused by many things, from the rotation of the Earth to the position of the Moon, and tidal effects can be seen not just in the ocean tide itself, but in rivers, lakes, and currents, and even on the Earth's surface. A common name for a tsunami is a "tidal wave," although these earthquake-caused surges of ocean water don't actually have any connection to tides.