Hi Scorpion99,
In Office 365, Office Web Apps is used from SharePoint Online. Office Web Apps make it easier for you to work in the cloud because they open Word, Excel, PowerPoint, and OneNote documents in your web browser, and documents are stored online in SharePoint sites.
For more information about Office Web Apps in Office 365, you can download the Microsoft Office Web Apps Service Description in the following link:
www.microsoft.com/.../details.aspx
Thanks,
Nancy Xie