Tides refer to the daily rising and falling levels of the oceans' surfaces.
They are caused by the gravitational pull of the moon and the sun on the ocean.
The tide rises and falls twice everyday.
When the earth, sun and moon are all aligned, the high tides are much higher than normal and the low tides are much lower than normal. These are called spring tides.
When the sun and moon are at a right angle to Earth they pull in different directions and there is only a small difference between high tide and low tide. These are called neap tides.
The times and heights of tides change everyday and also vary from place to place.
