A Microsoft file hosting and synchronization service.
This is from the article:
Important: The Add to my OneDrive option isn't available when:
- You're signed in with a work or school account. Instead, you'll see Add shortcut to OneDrive.
- You've already added the folder to your OneDrive, or you have more than one folder selected. (You can't add multiple folders at the same time.)
- The item you're trying to add isn't a folder. (Add to my OneDrive isn't available for individual files or for collections of files such as albums.)
You can ask OneDrive support at https://support.microsoft.com/enus/contactus/onedrive/tech-services/