A set of terms and conditions that a user must agree to before signing up for a service. These are the long blocks of legalese you have to wade through before you sign up for your ISP, email provider, or web host. Usually, failure to abide by the Terms of Service (or ToS) results in cancellation of the service and deletion of your account.

In its abbreviated form, ToS is also used as a verb, to describe the deletion of an account for breaking the rules. "Geocities ToS'ed me for putting bomb-making instructions on my web site!"