What is a cylindrical recess around a hole usually to receive a bolthead or nut?

A cylindrical recess around a hole designed to receive a bolthead or nut is known as a counterbore. This feature allows the head of a bolt or nut to sit flush with or below the surface of the material, providing a cleaner appearance and preventing snagging. Counterbores are often used in applications where a smooth surface is essential or where additional components may need to be installed over the fastener.