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A liquid is a state of matter in which the molecules are constantly moving and colliding with each other. The molecules are held together by intermolecular forces, which are much weaker than the intramolecular forces that hold together atoms in a solid. liquids have a definite volume but no fixed shape. They flow to take on the shape of their container.
Liquids are found in nature as water, blood, milk, air (humidity), oil, mercury, etc. They have numerous applications in industry and technology: they are used as coolants, lubricants, solvents, adhesives etc.
The study of liquids is known as fluid mechanics. Important concepts in fluid mechanics include surface tension, viscosity and hydrostatics.