This means something feels smooth, moisturizing, emollient, and not waxy, draggy, thin, or too greasy. One textbook defined smooth as “slippy, slippery, velvet, flowing”, and moisturizing as “oily, wet, heavy, moist”. (Reference, Formulas, Ingredients, and Production of Cosmetics) In general, it means an ingredient that feels rich and emollient, so thinner ingredients, like fractionated coconut oil or isopropyl myristate, wouldn’t be considered lubricious. Our liquid oils are considered lubricious, while solid oils with shorter fatty acid chains and some butters are considered “coarse”. Waxes are considered draggy and “adhesive”.
Surfactants can be considered to be lubricious if they feel rich and creamy, like the elegant foam and lather we get from sodium cocoyl isethionate (SCI) when compared to foaming silk protein, which has a lacy glove lather.