I am learning about black body radiation and it was stated in a textbook that
The best model for a black body is a large cavity with a very small hole in it which absorbs all incident radiation. The radiation hits the walls and rattles around inside and comes to thermal equilibrium with the walls before emerging from the hole.
However, the definition for a black body is an object that absorbs all incident radiation. In this case, for incoming radiation that did not hit the hole but the external walls of the cavity, they could either be reflected or absorbed. How then is the cavity a black body?