The three primary states of matter include the solid-state, the liquid state, and the gaseous state. In solids, the individual particles are tightly packed with not much scope for movement. This is the reason why solids have a definite volume and a definite shape. In liquids, the individual particles are packed relatively less tightly (when compared to solids). This is the reason why liquids do have a definite volume but do not have any definite shape. They tend to assume the shape of the container they are placed in. Finally, gaseous substances feature spaced-out arrangements of the constituent particles. Therefore, gaseous substances do not have any definite volume or shape.
It is important to note that the three different states of matter are interchangeable and the physical state of a substance is dependent on the absolute temperature and pressure of its surroundings. Generally, when a solid is heated to a specific temperature, it is converted into a liquid (which can be further heated into a gas).