The term 'hollow space' can be described as a CAVITY, which is a six-letter word. A hollow space is an empty area or void within a solid object or material. It can also refer to a gap or depression in a surface, such as a cave or a hole in the ground. Hollow spaces are often used for storage, insulation, or to create a soundproof environment. They can also be used to create a visual effect, such as a window or a doorway.