"Sorbitan" refers to the ingredient sorbitan hydride. Sorbitan consists of a mixture of several isomeric cyclic compounds, which are formed by the splitting off of a molecule of water from sorbitol. "Diisostearate" means the diester of isostearic acid.
Sorbitan diisostearate is used in cosmetic formulations. The sorbitan fatty acid ester acts as an emulsifier (a surface-active substance which is used as an additive in cosmetic products to combine two immiscible liquids - e.g. oil and water - to form an emulsion).