How to install and upgrade Office Online Server to the latest version
Office Online Server (OOS) is the next generation of Office Web Apps Server (OWA), which allows organizations to deliver browser-based versions of Word, PowerPoint, Excel and OneNote, among other capabilities.
Most people who need to run Office Online Server are having Skype for Business Server 2015/2019 or SharePoint. Within Skype for Business it will be used for PowerPoint presentations inside meetings.
You can download Office Online Server from MSDN or Volume Licensing Center.