Reagent

A reactant (including reactant in older literature reagent or starting material ) is a substance that is consumed in the course of a chemical reaction.

As reactants both elements and chemical compounds can be used. In the chemical industry products are specifically produced from reactants. Therefore, such substances are also referred to as starting materials. In chemical equilibrium, the distinction between reactant and product is no longer meaningful.

Demarcation

In the catalysis and enzymology of a starting material is also called substrate.

The metabolism is also spoken of precursors.

The right chemicals called bases, with which one can produce banned or dangerous substances, precursors.