A Terms and Conditions agreement (T&C) is an agreement that outlines and sets forth your rules and requirements for people who use your website or mobile app.
Topics addressed in a T&C include such things as acceptable behavior by users, restricted uses of your service and the maintenance of your rights, such as the right to terminate access to people who violate your rules. Users must agree to your Terms and Conditions for them to be enforceable.
Terms and Conditions agreements are also known as Terms of Service or Terms of Use agreements. The name doesn't matter, as they all serve the same purpose: Protecting your business and keeping your users informed.