Presence of a Catalyst
There are two types of catalysts and they work to increase the rate of reactions in two different ways.
We will call the first type of catalyst a surface catalyst. These are often called heterogeneous catalysts because they are often in a phase other than the one the reactants are in. In other words, surface catalysts are generally solids and most reactions occur in either the liquid or gas phase (or as dissolved species in solution).
The other type of catalyst we will call a "get-involved" catalyst. There are often called homogeneous catalysts since they are usually in the same phase as the reactants.