Patient-friendly definition from the DentistsDirectory.org dental glossary.
A dental veneer is a custom-made, wafer-thin shell — typically 0.5–1.0 mm thick — bonded permanently to the visible front surface of a tooth to improve its colour, shape, size, or surface texture. Veneers are primarily a cosmetic treatment and are most commonly placed on the upper front teeth (the "smile zone" teeth visible when speaking or smiling). Porcelain veneers are the most common type; composite resin veneers are a less expensive, more repairable alternative.
Veneers are an excellent solution for a range of cosmetic concerns on otherwise healthy teeth: intrinsic discolouration that does not respond to bleaching (such as tetracycline staining or fluorosis); teeth that are chipped, fractured, or worn; minor misalignment or spacing where orthodontics is not desired; teeth that are too small or irregularly shaped; and uneven smile aesthetics where some teeth are disproportionate. They are not appropriate for teeth with significant structural damage, active decay, or insufficient enamel, or for patients with severe bruxism without proper bite management.
The most important thing to understand about porcelain veneers is that the preparation process is irreversible. A thin layer of enamel — typically 0.5–0.7mm — is permanently removed from the front of the tooth to create room for the veneer and prevent it from looking bulky. Once this enamel is removed, the tooth requires coverage for life. This is not a reason to avoid veneers when they are appropriate, but it does mean the decision warrants careful consideration. Composite veneers (direct bonding) are an alternative that can be placed with minimal or no tooth reduction and are reversible, though less durable than porcelain.