flow, stream, category

流 is composed of the radical of 水 (water) and 㐬 (flow). 㐬 means the movement of liquid, and the 水 component emphasizes this original sense. In addition to meaning the movement of liquid, 流 is also used to indicate the movement of other things. Moreover, when a large river rushes forward, it branches into multiple smaller channels. Therefore, 流 also carries the meaning of category, type, or rank.