A small, three amino acid synthetic tripeptide with a molecular weight smaller than 500 Da (500 Da is often referred to as the limit for proper skin penetration).
The manufacturer claims that it can boost the synthesis of hyaluronic acid in the skin (up to 300% based on in-vitro tests) that is important for proper skin hydration and plumpness. It can also improve collagen fiber quality by increasing some structural skin elements (so-called proteoglycans), like decorin and lumican.
The peptide is suggested for firming and remodelling treatments, as well as against skin sagging. It's also marketed as a "needle-free hyaluronan booster".