Most enzymes are
proteins
Enzymes are proteins that facilitate biochemical reactions. Proteins are large biomolecules, or macromolecules, consisting of one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalyzing metabolic reactions, DNA replication etc.
They are often referred to as catalysts because they speed up chemical reactions. Pepsin is a digestive enzyme that works in the stomach to break down proteins in food.