A Microsoft file hosting and synchronization service.
Hello,
OneDrive could be a backup software, but only if you had enough storage to backup an entire system.
As Palcouk said, OneDrive isn't included in Office 365 because Office 365 is for one computer as a one-time purchase. You get 5 GB of free data on plans that aren't on Microsoft 365, so to Microsoft, it's as if you're not paying for OneDrive (because technically you aren't), and that your OneDrive account is a free plan.
OneDrive is only available for free, basic, or premium/personal and family subscriptions for Microsoft 365 because Microsoft is trying to entice you into buying a plan that can hold more storage than free.
If you don't want to buy Office 2024, subscribe to Microsoft 365 you would probably spend the same amount of money for every new major edition of Office as you would by subscribing to Microsoft 365.
Hope this helps.