Rate limiting is a security measure that restricts the number of requests an IP address or client can make within a given timeframe, preventing malicious users from overwhelming servers with too many requests and reducing the risk of denial-of-service (DoS) attacks and abuse. This can be implemented using the `express-rate-limit` library in Node.js, which makes rate limiting easy and efficient by allowing configuration of various options such as max requests, window time, and custom headers.