A salary cap is a limit set by a sports league on the total amount of money that a team can spend on player salaries in a given season. This system is designed to promote competitive balance among teams, ensuring that wealthier teams cannot simply buy all the best players, which would create an uneven playing field. In leagues like the NFL or NBA, the salary cap helps maintain fairness by requiring teams to manage their budgets effectively. Teams must strategize to build a competitive roster while staying within the cap, which can lead to more exciting and unpredictable games.