A Microsoft file hosting and synchronization service.
If you have Microsoft 365 Business Premium plan, you can't add extra storage to the existing plan, but you can purchase additional plans to increase this storage up to 5TB, like OneDrive for Business (Plan 2).
Details at
https://www.microsoft.com/en-us/microsoft-365/onedrive/onedrive-business-plans-and-pricing
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hth
Marcin