河曲又称曲流，为河道弯曲，形如蛇行的河段，多见于河流的中下游。当河床坡度减小，河流的下蚀作用减弱，而侧蚀作用明显，河流不断地侵蚀河岸、扩展河床，致使河道发生弯曲，形成曲流。

Meander refers to the reach that bends like a snake, which usually can be found in the middle and lower reaches of rivers. As the gradient slackens, the erosion effect of the river decreases, while the lateral erosion effect become more obvious. As a result, the river constantly erodes the river bank and expands the riverbed, causing the river to bend and forming meanders.