What does fair usage policy mean?

The answer

A fair usage policy is a rule that allows a plan to be called unlimited while placing a threshold on heavy use. After you cross the stated amount of data in a billing cycle, speed is usually reduced for the rest of that cycle, so the connection keeps working but video may buffer and big downloads take longer. Read the word unlimited together with the policy. Ask for the exact threshold in gigabytes, the reduced speed, the reset date and how to check your usage.