What is the term for the reactants in an enzyme catalyzed reaction?
A substrate is a reactant that is used by an enzyme. Substrate is a broadly used term, but it is mainly used when talking about biochemical functions.
In the general sense, substrates are the chemical species being observed during the reaction (i.e. your reactants). In the biochemical sense, this is the molecule that the enzyme is reacting with.
Substrates can be found in different types of applications. It just depends on the context.