tributary; branch of a river
Literal geographical use: a smaller stream that flows into a larger river.
この川の傍流はいくつかある。
This river has several tributaries.
Figurative use: a branch, faction, or school of thought that is not part of the mainstream. Often contrasted with 主流 (mainstream).
See also: 主流
彼の意見は学界の傍流に過ぎない。
His opinion is merely a fringe view in the academic world.
その政党の傍流が新しい政策を提案した。
A faction within the party proposed a new policy.
主流 refers to the dominant mainstream faction or trend, while 傍流 refers to a minor, non-mainstream branch or faction.
Compound of 傍 (side, nearby) and 流 (flow, current). The literal meaning 'side stream' extended to figurative uses for non-mainstream groups or ideas.