A name or identity, ID for short, is your home on the decentralized internet. Your identity is unique, like a passport number, only you have it. To use an application, you sign into the application with your identity and a secret key only you know.
Your data and where it is stored is connected with your identity. When you sign into a DApp, you give the DApp permission to read your data and write to your data store on your behalf. When you log out of an application, it no longer has access to your data or data store — until the next time you log in with your identity.