Liquid, a state of matter with properties midway between those of solids and gases. Water is the most familiar liquid. Liquid molecules have more cohesion (mutual attraction) than gas molecules but less than solid molecules. Hence, unlike a gas, a liquid has a definite volume; but unlike a solid, it has no fixed shape. It is shaped by its container.

Cohesion accounts for surface tension. The surface molecules of a liquid, drawn to each other and pulled down by those below, behave like a stretched elastic membrane. Surface tension, combined with adhesion (the attraction of molecules for other substances) explains capillarity, the tendency of liquids to rise in narrow tubes.

Liquids may evaporate, boil, condense, freeze, and form solutions. They are capable of diffusion and osmosis, and of transferring heat by conduction and convection. Liquids flow, but they also have viscosity (resistance to flowing). They also possess buoyant force.