All matter consists of particles which are

1. in constant motion and
2. attracted to one another.

Matter is anything has has mass and occupies volume. It exists in three main physical states - solids, liquids and gases.

Solids consist of particles packed closely together in a crystal lattice vibrating in fixed positions in a crystal lattice. Solids have a fixed volume and retain their shape.

Liquids consist of particles that are close together and are moving over one another. Liquids have a fixed volume and fill the shape of their container.

Gases consist of particles that are far apart and that moving past one another. Gases have a variable volume and fill the shape of their container.