A rear hub in which the sprocket is rigidly connected to the hub, without a freewheel The pedals of a fixed-gear bicycle revolve whenever the rear wheel turns; coasting is impossible This type of gearing is usually associated with track racing See my article on fixed-gears
A direct drive system, used on track bikes, in which the chain ring and rear cog are linked, so that the pedals turn constantly while the bicycle is moving, and coasting isn't possible