What is the definition of a door?

A door is defined as a moveable barrier used to cover an opening. This definition captures the primary functional aspect of a door, which is to provide access to different spaces, while also allowing for privacy and security when closed.

In practical terms, doors can be opened and closed, facilitating entry and exit from rooms, buildings, or enclosed areas. They serve various roles, such as controlling airflow, blocking noise, and enhancing safety. The design and mechanism of doors can vary widely, including traditional hinged doors, sliding doors, and bi-fold doors, but they all share this fundamental purpose of serving as a movable barrier.

The other choices may describe components related to doors or aspects of their functionality but do not accurately encompass the entire definition. For instance, while a door can help block sound, that is not its primary definition. A fixed panel does not relate to the moveable nature of a door, and a permanent structure for walls is unrelated to the concept of doors altogether, which are inherently designed to be operable.