A rim brake is a type of bicycle brake that works by applying friction to the outer edge of the wheel's rim. When the brake lever is pulled, brake pads press against the rim, slowing down or stopping the bike. Rim brakes are commonly found on road bikes and some mountain bikes due to their lightweight design and simplicity. These brakes are typically easier to maintain and adjust compared to other systems, such as disc brakes. However, they can be less effective in wet conditions, as water can reduce friction. Overall, rim brakes are a popular choice for many cyclists for their reliability and ease of use.