For questions about dropouts on bicycles. Dropouts are a kind of fork end where the wheels are attached; we often use "dropout" for any slot to hold the axle at the end of forks, but strictly speaking, a dropout is a fork end where the wheel can be removed from the frame without taking the chain off first.

A type of fork-end which allows the rear wheel to be taken off without derailing the chain first. This is found at the rear of the bike, near the centre of the rear wheel, it is the part of the frame which the wheel is supported by.