Solids have a definite shape and volume. Liquids have a definite volume, but take the shape of the container. Gases have no definite shape or volume.
Solids have a fixed shape and a fixed size. The particles are very close together and held in place by strong forces (bonds). Their particles cannot move around, but they do vibrate. Because the particles cannot move around, a solid has a fixed shape.
Solids can be hard like a rock, soft like fur, a big rock like an asteroid, or small rocks like grains of sand. The key is that solids hold their shape and they don't flow like a liquid.
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