A Terms and Conditions can be used for both your website and your mobile app. It’s not required or recommended to have separate agreements, one for your website and one for your mobile app.
This agreements act as a contract between you (the company) and the users who are using and accessing your web site.
The simplest definition for this kind of agreement would be:
Terms and Conditions are rules which one must agree to abide by in order to use a service.