Liquids are one of the three primary states of matter, alongside solids and gases. They have a definite volume but no fixed shape, allowing them to take the shape of their container. The particles in a liquid are close together but can move freely, which gives liquids the ability to flow. Common examples of liquids include water, oil, and juice. Liquids can be classified as either pure substances, like water, or mixtures, such as saline solution. The behavior of liquids is influenced by factors like temperature and pressure, which can change their properties and states.