A gizmo is a small piece of equipment when you cannot remember, or do not know, its real name. “Pass me that gizmo” means “that little thing that does a job.” It is informal, more American than British (British speakers often say gadget or thingy). It can sound playful, and a little helpless: you know what it does, not what it is called. It is not a technical word. An engineer would use the proper name. People also stretch it for any small clever device, even when they could name it if they tried.

小玩意、那個小裝置（叫不出正式名稱時）