A semifinal is one of the matches or competitions that determine who will compete in the final round. In many tournaments there are two semifinals, and the winners of those two semifinals face each other in the championship, while the losers are eliminated.

Think of a tournament bracket: if eight teams start competing, they play until four remain, then two, then one champion. Those matches where four teams become two? Those are the semifinals.

In sports like basketball or soccer, making it to the semifinals means you're among the final four competitors, which is a major achievement. A spelling bee might have semifinals where the best spellers compete before the championship round. A science fair could have semifinals where judges select the top projects for final evaluation.

Sometimes you'll hear semifinals called the “final four” (especially in college basketball) because four teams or competitors remain. Reaching the semifinals means you've already beaten most of your competition. You're two wins away from being champion: one to get through the semifinal, and one to win the final.