Here's a breakdown:

* Enzymes are biological catalysts that speed up chemical reactions within living organisms.

* Catalysts don't get consumed in the reaction, but they facilitate the reaction by lowering the activation energy required.

* Reactants are the starting materials for the reaction.

* Product is the molecule that is formed as a result of the reaction.

For example:

* The enzyme lactase breaks down the reactant lactose (a sugar) into the products glucose and galactose.

It's important to remember that enzymes are highly specific, meaning that they only catalyze a single reaction or a small set of related reactions. The product of an enzyme is determined by the specific reaction it catalyzes.