Office Online in Office 365 comes as a subscription solution, which you can scale up or down according to the need of your business.
Microsoft Office Online allows you to work in Office files everywhere, and on almost any device. Spreadsheets, presentations, notebooks, Word, Excel, PowerPoint and OneNote files can be opened in your web browser, so you can continue working on your files right wherever.
You can do the same things as in the desktop version i.e. create, edit and share documents – however, everything is gathered online.