Anything that has mass and volume is called matter. There are four classical states of matter: solid, plasma, liquid and gas. Each type of matter has different properties.
In a solid, the object's particles are close together. Solids also have a fixed volume. Plasma is a mixture of charged ions, free electrons and neutral atoms. The charged particles give plasma the ability to generate and respond to electromagnetic forces.
The particles in liquids are close together, but they are also free to move around. Liquids have a fixed volume, but they do not have a fixed shape. The shape of a liquid depends on the shape of its container. A gas does not have a fixed shape or a fixed volume. Instead, it takes on the shape and volume of its container. The molecules in gases are in constant motion.
In modern physics, there are around 18 distinct forms of matter, each with different properties. Many of them are ultra-low-energy states of matter.