A veneer is, quite simply, a porcelain "jacket" that sits over the tooth and makes it look like new. Veneers are used for various reasons, primarily to improve the appearance of a tooth but also to cover damage.
A small section of the tooth enamel is shaved away to make room for the veneer, the veneer is then bonded to the tooth with permanent adhesive. Patients can then eat and drink as normal, however the life of the veneer is preserved by good dental hygiene, as can be said of a normal tooth.
For more information on veneers, click here (requires Adobe Acrobat).