A rate limit puts a cap on how much, and how fast, you can use a company’s API. They’re usually structured as a max number of requests per second.
Rate limits help developers protect against spammers (or scammers) abusing their APIs, but they also help them keep a check on the infrastructure the API is running on and make sure it doesn’t get overwhelmed. Here’s an example from X, where each endpoint has different rate limits depending on which plan you’re on.