The moon's gravity pulls at the Earth, causing predictable rises and falls in sea levels known as tides. To a much smaller extent, tides also occur in lakes, the atmosphere and within Earth's crust. High tides refer to water bulging up from Earth's surface, and low tides when water levels drop. High tide occurs on the side of the Earth nearest the moon due to gravity, and on the side farthest from the moon due to the inertia of water. Low tides occur between these two humps.

Source: Space