CEREC is a machine dentists use to manufacture tooth restorations, like crowns and veneers. It's an acronym which stands for Chairside, Economical Restorations of Esthetic Ceramic.
Chairside means the dentist can provide the treatment (crown, veneer, etc) in one patient visit and Ceramic refers to the final product - a non-metallic restoration which is bonded to the existing or remaining tooth structure. As such, CEREC restorations are extremely durable and natural looking.
Many studies have shown CEREC restorations to last as long as Gold restorations (long the industry standard for quality and longevity).
The benefit to patients is treatment in one appointment and a tooth-colored restoration which matches the look and feel of their natural teeth.