A FIXIED GEAR BIKE or FIXIE is a single speed bike without the ability to freewheel or ‘coast’. The rear cog is attached or ‘fixed’ to the bike’s rear wheel which means whenever the bike is in motion, the pedals will go around. When the rear wheel turns, the pedals turn in the same direction, so you're always pedalling on a fixed-gear bicycle.
Fixed-Gear bicycles are also counted as single-speed bicycles—bicycles without derailleurs, with a single sprocket attached to the rear hub, and a single sprocket attached to the crank.
The fixed-gear single-speed bicycle is the most basic type of bicycle.
In Australia, "fixed-wheel" is the normal term for the subject of this article—meaning the opposite of freewheel, and "fixed-gear" usually refers to a single-speed bicycle.
There are some fixed wheel bikes completed with a Flip-Flop Hub which takes both - normal single speed and fixed gear sprockets letting you choose which one to ride.
Please also see our articles on Single Speed Bike Explained and Flip Flop Hub Explained.