fast lens refers strictly to the maximum light gathering ability at the largest aperture size of a lens to gain maximum shutter speed given the various lighting condition, but regardless of ISO and filters. it relates directly to the maximum aperture size a lens is designed (with acceptable optic quality)
fast camera is less commonly used as a term, but can be referred to as per its processing speed, i.e. starting up, shutter lag, writing speed, speed in handling in camera processing such as noise reduction.
autofocus is a combined effort from the body and lens. i may not fully understand this as it is often not quantified (or maybe it is, but not to my limited knowledge)
any seniors or professionals here, pls correct me if i'm wrong.