A peptide is a molecule consisting of two or more amino acids. Peptides are smaller than proteins, with the division between the two being about 50 amino acids. Amino acids are linked by a peptide bond, called dipeptide, tripeptide, and so on, depending on the number of amino acids present.
Many hormones are peptides, including all those secreted by the pituitary gland. Many different peptides (often called neuropeptides) are also made by subpopulations of neurones in the central and peripheral nervous systems.