Peptides are like proteins, but smaller. The formal definition is “two or more amino acids linked in a chain”. The lines are a little blurry, but peptides are typically 2-49 linked amino acids and proteins are 50+. Insulin is a peptide hormone and the first peptide developed/discovered.
Currently the most popular uses of peptides are to stimulate collagen production, sleep, anti-aging properties, muscle growth, immune support, and neurologic support.