Waxes are a biologically important category of lipids. Wax covers the feathers of some aquatic birds and the leaf surfaces of some plants, where its hydrophobic (water-repelling) properties prevent water from sticking to, or soaking into, the surface. This is why water beads up on the leaves of many plants, and why birds don’t get soaked through when it rains.
Structurally speaking, waxes typically contain long fatty acid chains connected to alcohols by ester linkages, although waxes produced by plants often have plain hydrocarbons mixed in as well.