An enzyme is a biological catalyst, but there are also inorganic catalysts. Enzymes are globular proteins synthesized within cells to catalyze specific chemical reactions. Inorganic catalysts are mineral ions or other small molecules not synthesized by the cell, and can facilitate chemical reactions.
An enzyme can only facilitate one specific type of reaction. For example, the enzyme lactase only breaks down lactose, and diastase only breaks down vegetable starch. Enzymes act by lowering the activation energy required for a specific reaction to occur. A catalyst, whether organic or inorganic, speeds up a chemical reaction, but it is not consumed by the reaction and can be used repeatedly.