Choking is examined in terms of its definitions. Three choking initiation mechanisms are identified : type A (accumulative) choking occurs when solids start to accumulate at the bottom of the conveyor as the saturation gas carrying capacity is reached; type B (blower-/standpipe-induced) choking results from instabilities due to gas blower-conveyor or solids feeder-conveyor interactions where there is insufficient pressure or too limited solids feed capacity to provide the needed solids flow; and type C (classical) choking corresponds to a transition to severe slugging. Approaches for predicting the onset of each of these type of choking are recommended. Implications for regime transitions in fast fluidization are also identified.