A Fair Usage Policy (FUP) is a provider rule set that limits apparently unlimited services so a small number of heavy users cannot degrade performance for everyone else. In hosting, cloud, and SaaS products, it may cap bandwidth, storage, CPU time, email sending, API calls, or background tasks even when the plan is marketed as “unlimited.” The exact limits are often written in policy language rather than shown as a hard technical ceiling.
In cyber security, FUPs matter because they help prevent abuse such as spam campaigns, bot-driven scraping, brute-force attempts, and resource-exhaustion attacks. They also protect shared infrastructure from one tenant consuming disproportionate resources. Defenders use these policies together with rate limiting, anomaly detection, and account review to spot suspicious behavior. Attackers may try to stay just below thresholds, rotate accounts, or exploit vague wording, so security teams should read FUPs as operational controls, not marketing slogans.