Terms of service are the legal agreements between the provider of a service—such as a website—and the users of the service. When a user is given proper notice of these terms and agrees to or accepts the terms by some affirmative act, such as continuing to use the service or ticking a box to indicate agreement, the parties form an enforceable contract regarding the user’s use or purchase of the product or service. Terms of service are also commonly referred to as terms of use, terms and conditions, or abbreviated as TOS or T&C.

In Pennsylvania, as in other states, terms of service (TOS), also known as terms of use or terms and conditions, are considered legally binding contracts between a service provider and the user, provided that the user has been given proper notice and has accepted the terms. Acceptance can be indicated through an affirmative act such as checking a box, clicking an "I agree" button, or simply by continuing to use the service. These agreements typically cover aspects such as the rights and responsibilities of the user, intellectual property protection, warranty disclaimers, limitation of liability, and dispute resolution procedures. For the contract to be enforceable, it must meet general contract principles, which include offer, acceptance, consideration, and the capacity to contract. Pennsylvania courts will enforce terms of service agreements that meet these criteria, provided they are not unconscionable, overly burdensome, or contain illegal provisions.