A fixie bike has no gears and generally has a fixed wheel which means if the wheels are spinning, you’re pedalling. No coasting along on these bikes. Fixie bikes are best suited to flat ground. Hills can be a problem for fixie bikes as they have no gears to help you climb. It doesn’t get much easier on the way down on a fixie as you have to keep those pedals spinning regardless of how fast you’re going. Fixies can often be referred to as fixed gear or fixed wheel bikes.
The fixie has become something of a fashion accessory or urban badge of honour in recent times. They are essentially a track bike, but a fixie is not intended for use on the velodrome, more the tight streets and lanes of a major city. Having no gears means that fixie bikes are simple, easy to maintain and have very little that can actually go wrong with them.