"Palmitoyl' means the univalent radical derived from palmitic acid (hexadecanoic acid), characterised by the loss of the hydroxy group, 'rheum rapontichum root extract' means the root extract of Rheum rapontichum (see there), the rhapontiary rhubarb, also called false rhubarb.
The substance mixture is used in cosmetic formulations. It acts as an antioxidant (prevents or delays the decomposition of active agents and additives in extemporaneous formulations even at low concentrations).