What is a substance that speeds up the rate of a chemical reaction called?

A substance which speeds up the rate of a chemical reaction is called as catalyst. A catalyst enhances the rate of the reaction without itself being utilized in the reaction. A catalyst do so by lowering the activation energy.

A catalyst provides an alternate pathway which requires lower activation energy for the reaction to proceed and form reaction products.

Metals like Nickel (Ni), Iron (Fe) etc are some examples of catalysts.

In biochemical reactions, enzymes do the same work as that of catalysts with the only difference that enzymes can be regulated but catalysts can't be regulated.

Best example of enzyme is catalase.