How are oligopeptides different from polypeptides?

In biochemistry, the distinction between oligopeptides and polypeptides is primarily based on the number of amino acid residues within the chain.123

• Oligopeptides: These are defined as relatively short chains containing a "few" amino acids. While definitions can vary, they are often categorized as having between 2 and 20 amino acids. Some sources broadly define them as small polymers consisting of fewer than 50 amino acid residues.123
• Polypeptides: These are longer molecular chains composed of "many" amino acids. They are typically defined as chains containing 50 or more amino acid residues.123

While these terms describe the length of the peptide chain, the boundary between them is not universally rigid. Furthermore, proteins are essentially large polypeptides or combinations of multiple polypeptide chains that often adopt complex secondary, tertiary, and quaternary structures, whereas peptides generally lack such well-defined, complex conformations.123