in Mathematics, a part of some solid body which is separated from the rest.

The frustum of a cone is the part that remains when the top is cut off by a plane parallel to the base. It is likewise called a truncated cone.

The frustum of a pyramid is also what remains after the top is cut off by a plane parallel to its base.

The frustum of a globe or sphere is any part of it which is cut off by a plane. The solid contents of it may be found by the following rule: To three times the square of the semidiameter of the base add the square of its height; then multiply that sum by the height, and this product multiplied by $\frac{1}{3}$ gives the solidity of the frustum.