A fixed-gear bicycle, often called a "fixie," is a type of bike that has a drivetrain with no freewheel mechanism. This means that the pedals are always in motion when the bike is moving, allowing the rider to control speed and braking by pedaling backward. Fixed-gear bikes are popular for their simplicity and lightweight design. Riders of fixed-gear bikes often appreciate the direct connection between the bike and the rider, which can enhance the cycling experience. They are commonly used in urban environments and are favored by some cyclists for their minimal maintenance requirements and unique aesthetic appeal.