INCI: Panthenol (also "D-Panthenol", "Pro-Vitamin B5")
Converts to pantothenic acid — vitamin B5 — on the skin. Acts as a humectant and as an emollient, so it both attracts water and improves how the surface feels.
Common in products aimed at dry and sensitive skin, and in aftercare products generally.
On a label: usually mid-list. Frequently paired with glycerin.