Veneers were first introduced to the dental profession in the 1970's. In many respects, they are the dental equivalent of artificial nails: They are artificial teeth placed over your own to improve your smile's appearance and uniformity. Professionally custom-made dental veneers are bonded to the teeth, but removable (temporary or trial) veneers are used by dentists to "preview" a new smile.
Professionally applied veneers are not removeable. Patients can opt for removeable veneers to improve the look of their smile if they're unsure permanent veneers are the right choice for their smile or their wallet.