A Microsoft file hosting and synchronization service.
It is only an issue for individual or family accounts. There is no way to "upgrade" you account to a business account. You have to create a whole new business account and you can not use the information you used for your family or individual account. This is why so many people unfortunately have gone back to google and other providers for share ability. I'm hoping they (MS) will realize this soon and come up with a way to "upgrade" to business without having to change all your information.
Fingers Crossed, but not holding my breath.