Terms of service (abbreviated as "ToS" or "TOS")[1] are rules by which one must agree to abide by in order to use a service. Usually, such terms are legally binding. Certain websites are noted for having carefully designed terms of service, particularly eBay and PayPal which need to maintain a high level of community trust because of transactions involving money. Terms of service can cover a range of issues, including acceptable user behavior online, a company's marketing policies,[1] and copyright notices.[2] Some organizations, such as Yahoo!,[3] can change their terms of service without notice to the user base. [3]