Lacquer is a type of hard and usually shiny coating or finish applied to materials such as wood or metal. It is most often made from resin extracted from trees and waxes and has been in use since antiquity.

Asian lacquerware, which may be called "true lacquer", are objects coated with the treated, dyed and dried sap of Toxicodendron vernicifluum or related trees, applied in several coats to a base that is usually wood. This dries to a very hard and smooth surface layer which is durable, waterproof, and attractive in feel and look. Asian lacquer is sometimes painted with pictures, inlaid with shell and other materials, or carved, as well as dusted with gold and given other further decorative treatments.

In modern techniques, lacquer means a range of clear or pigmented coatings that dry by solvent evaporation to produce a hard, durable finish. The finish can be of any sheen level from ultra matte to high gloss, and it can be further polished as required. Lacquer finishes are usually harder and more brittle than oil-based or latex paints, and are typically used on hard and smooth surfaces.

In terms of modern finishing products, finishes based on shellac dissolved in alcohol are often called shellac or lac to distinguish them from synthetic lacquer, often called simply lacquer, which consists of synthetic polymers (such as nitrocellulose, cellulose acetate butyrate ("CAB"), or acrylic resin) dissolved in lacquer thinner, a mixture of various organic solvents. Although synthetic lacquer is more durable than shellac, traditional shellac finishes are nevertheless often preferred for their aesthetic characteristics, as with French polish, as well as their "all-natural" and generally food-safe ingredients.