1.
tidal front, ocean current boundary
The boundary where two ocean currents meet, often visible as a line on the water's surface. Important in fishing as fish tend to gather at these boundaries.
2.
turning point, shift in the tide
A figurative turning point or moment when the direction of events, public opinion, or a situation changes decisively.
Usage
The figurative sense (turning point) is extremely common in news and political commentary. The phrase 潮目が変わる (the tide turns) is the most frequent usage pattern, used for shifts in elections, markets, public sentiment, and negotiations.
Similar words
転機 (turning point) is a more general term. 潮目 specifically evokes the metaphor of ocean currents and implies a large-scale, decisive shift rather than a personal turning point.