Here's a breakdown:

* Matter: Anything that has mass and takes up space (i.e., has volume).

* Chemical Reaction: A process where substances are transformed into different substances by breaking and forming chemical bonds.

In simpler terms, the law means that during a chemical reaction, the total amount of matter present before the reaction must equal the total amount of matter present after the reaction. Atoms are just rearranged, not created or destroyed.

Example:

When you burn wood, the wood appears to disappear. However, the wood hasn't vanished; it has been transformed into ash, smoke, and gases. The total mass of the wood, ash, smoke, and gases is the same as the original mass of the wood.

Important notes:

* This law applies to ordinary chemical reactions, not nuclear reactions. In nuclear reactions, matter can be converted into energy and vice versa (as described by Einstein's famous equation E=mc²).

* The law of conservation of matter is a fundamental principle in chemistry and physics.