Final answer:
A coffer or lacunar is a recessed, usually square or octagonal panel in a ceiling, soffit, or vault, used in classical and neoclassical architecture.
Step-by-step explanation:
The term used to describe one of a number of recessed, usually square or octagonal panels in a ceiling, soffit, or vault is known as a coffer or lacunar. These decorative features can be seen in various forms of classical and neoclassical architecture. They are not just aesthetic but can also reduce the weight of the ceiling or vault. The coffered ceiling is a classical architectural design characterized by a series of indented squares that decorate the ceiling. This style is similar to the indented texture provided by fluting on a column or pilaster. While coffers serve as a significant decorative element, other architectural features like ribbed vaulting not only add beauty but also support the structure above. Coffered designs are often associated with grand buildings and are a hallmark of grandeur and sophistication in architectural design.