Refers to the dominant trend, flow, or current in a field, such as thought, culture, or oceanography. Often used in formal or academic contexts.
His ideas go against the mainstream of academic circles.
The main current in this sea area flows southwest.
Compound of 主 (しゅ, 'main') and 潮 (ちょう, 'tide' or 'current'). The reading しゅちょう is a standard on'yomi combination.