In the manufacturing world, there are three classes of clearance. Slip clearance allows one part to freely move past the other part. This is used to create assemblies that fit together with room for movement, like how a shaft turns in a bushing or a door fits within a door frame as it closes. Transition fits are used in parts that need to fit tightly together but will be removed in the future. This fit is used to align a gearbox and engine or in the lens of your camera. Interference fits could be confused with not fitting at all, but they must be calculated precisely to not deform material. These are commonly known as press fit parts and require a ram or hydraulic press to permanently install parts.