Here's what it means:

* Matter is neither created nor destroyed in chemical reactions. The total mass of the reactants (the substances that react) is equal to the total mass of the products (the substances formed).

Example:

Imagine burning wood. The wood appears to disappear, but it hasn't vanished. It's been transformed into ash, smoke, and gases. If you could carefully collect all of these products and weigh them, you'd find their combined mass is equal to the original mass of the wood.

Important Points:

* Chemical Reactions: The law applies specifically to chemical reactions, where the atoms within molecules are rearranged. Nuclear reactions, which involve changes in the nucleus of atoms, are not covered by this law.

* Conservation of Atoms: The law of conservation of mass is ultimately a consequence of the conservation of atoms. In a chemical reaction, the atoms are simply rearranged, not created or destroyed.

Let me know if you'd like more examples or have any further questions!