A Rate Limiter is a tool used in computer networks and applications to control the amount of incoming or outgoing traffic. It helps prevent overload by restricting the number of requests a user can make to a server within a specific time frame. This ensures that resources are used efficiently and that the system remains responsive. Rate limiters are commonly used in APIs, where they help manage the load on servers and protect against abuse or denial-of-service attacks. By setting limits, developers can ensure fair usage among users and maintain the overall performance of the system, benefiting both users and service providers.