Matter is anything that occupies space and has mass.
There are three states of matter namely:
Solid is the kind of matter with definite shape and volume do not change unless force is applied on them. The molecules of the solids are closely packed.
Liquid is the kind of matter with definite volume but no definite shape. They assume the shape of the container. The molecules of liquids are far apart.
Gas is the kind of matter with no definite volume and shape. It assumes the shape and volume of the container. The molecules of gases are very far apart and move freely.