Office 365 primarily denotes a set of subscription based software services that require monthly or periodic payment of fees to Microsoft Corporation. By contrast, Office 20XX generally refers to a suite of desktop applications that alone by themselves are not subscription based and do not carry monthly fees.

Although Office 365 also often refers to cloud-based services rather than desktop applications, certain Office 365 subscription plans include a subscription to Office 20XX desktop applications in addition to cloud-based services. The subscription to Office 20XX desktop applications, by virtue of the subscription, makes the subscription part of an Office 365 offering.

Office 365 was initially announced in the autumn of 2010, and was made available to the public on June 28, 2011. The initial subscription plans included a Professional plan (for organizations of 25 and smaller) and an Enterprise plan (for organizations with more individuals).