The particles of solids are more closely packed then those of a liquid or gas, because force of attraction is stronger in solids then in a liquids or gas. Solids have definite volume and definite shape. Gas particles are freely moving, and they are not closely packed and it can take any shape, while in liquid they are packed closely and it has only definite volume that can take a shape of container, while in solids particles are packed in order which makes them solid.
There are two types of solids:
Crystalline Solids they consist crystals.
Amorphous Solids in which particles are arranged randomly.