Like any sport, tennis has its own language. One term that can help you better understand the game and how it's scored is break point.
A break point occurs when two conditions are met: 1) one player is one point away from a win, and 2) their opponent is serving. Essentially, in order to win the game - and inch closer to winning the set and match - the player must "break" their opponent's serve. There are four possible scoring combinations that could give rise to a break point: 0-40, 15-40, 30-40, or when the server does not have the advantage in a deuce. (A deuce occurs when the score is tied 40-40. To break the tie, someone must score two points in a row. A player gains the advantage when they've scored one.)
Winning the break point means winning the game, but it's not as easy as it sounds. It's harder to win when your opponent is serving, because a strong serve can put the returner on the defensive or disrupt their strategic placement. That's why a break point is a particularly tense moment: you've got one person with the scoring advantage but not the serving advantage, and another person trying to seize their last chance to keep the game alive - sometimes with an Olympic medal on the line.