What is the meaning of "less dense as a solid than liquid" and how is it important to life on earth?

The water is an essential component of the life on the Earth. Certain properties of water makes it such a vital liquid required by all the life forms. Among the special properties of water, one is that it is less dense as a solid than liquid. It means that when water is present in it's solid form (i. e. ice), the density of it id less than its liquid form. It is because as the water freezes it expands. Other liquids becomes more dense when they freeze but water expands.

This property of the water is essential for the life forms as it makes the ice floats on the surface of water rather than making it sink. If the ice was denser than the water bodies would be all freezed up in winters and the life inside them would die.