the.com/swinging door

means A door hinged to swing open in either direction and fall shut again on its own, so you can pass through it without hands or a decision about which side it belongs to.

from Simply a straightforward compound of 'swing' (Old English swingan, to swing or sway) plus 'door' (Old English duru) — the name just describes what it does. It became common with restaurant and saloon kitchen doors in the 1800s and 1900s, fitted with double-action hinges so staff could push through with full hands; the Old West saloon's slatted 'swinging doors' are the image most people carry, though the mechanism itself is older and plainer than the cowboy myth suggests.