In gambling, and especially in poker, a shark is a highly skilled player who is markedly stronger than the opposition at the table. The term captures the predatory dynamic: sharks profit by exploiting the recurring mistakes of weaker players, who in the same imagery are known as fish. The label is about relative skill, so a player can be a shark at one table and merely average at another.
Much of a shark's edge comes from selection rather than spectacular play. In poker, deliberately seeking out games populated by weaker opponents is called table selection, or informally finding the fish, and it is one of the most reliable ways to raise win rate. A strong player who insists on battling other strong players forgoes much of the profit that the same skill would earn against softer competition.
The advantage is exercised through patience and discipline. A shark applies sound fundamentals, position, hand selection, bet sizing and reading opponents, consistently enough that small edges compound across many hands. The image of the aggressive bully is misleading; much of a shark's profit comes from quietly punishing predictable errors rather than from flashy bluffs. In casino games, the equivalent figure is the advantage player, such as a card counter or someone exploiting favourable rule variations.
The common misconception is that being a shark means winning every session.
Variance ensures that even the best players endure losing stretches, and a shark's superiority shows only over a large sample. The related mistake, for less experienced players, is overestimating their own edge and sitting in tough games where they are in fact the fish. Honest self-assessment and good game selection are as much a part of the shark's toolkit as technical skill.