Peptides are short chains of amino acids, the fundamental building blocks of proteins, acting as crucial signaling molecules that regulate bodily functions like metabolism, healing, inflammation, and hormone secretion. They are smaller than proteins (usually under 50 amino acids) and naturally occur in foods and the body, but synthetic versions are used in medicine for treating conditions like diabetes (e.g., insulin) or for anti-aging and muscle growth, though some have risks and require medical guidance.