This is Office that is connected to your microsoft account, of course you must have / create a microsoft account first to be able to download, install and activate your office,
What are the advantages of Microsoft Office Bind Key?
You can use Office Bind Key anywhere, just sign in with your Microsoft account at the office you want to use, but the office you use must be the same version as the Bind Key you purchased.
How to download, install and activate office bind key?
1. Visit the setup.office.com link
2. Sign in with your Microsoft account, or “Create New Account” if you don’t have a Microsoft account yet.
3. Enter the Product Key that you have purchased
4. Then you can download and install office online.
5. After the installation is complete, please open an office app and select the account menu, please sign in with a Microsoft account that is connected to the office bind key, then your office will be automatically activated.