公平使用原则是指互联网服务提供商会透过减慢其网络速度以对数据用量超出指定上限的客户施加限制。香港电讯管理局现已对公平使用原则作出管则。

A bandwidth cap, also known as a band cap or a data cap, limits the transfer of a specified amount of data over a period of time. Internet service providers commonly apply a cap when a channel intended to be shared by many users becomes overloaded, when the provider sees an opportunity to exploit their customers lack of competitive options or understanding of the services and technology. Implementation of a bandwidth cap is sometimes termed a fair access policy, fair usage policy, or usage-based billing.