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. In leagues like the NFL and NBA, the salary cap helps maintain fairness by preventing teams from dominating due to financial advantages. Teams must strategically manage their rosters and budgets to comply with the cap while still trying to build a competitive team.