Microsoft Stream is a cloud-based enterprise video service, that is included in many Microsoft Office 365 Plans. Now, Microsoft Stream is also available as Standalone Plans (Plan 1 & Plan 2).  This page is useful for comparing the features of the two plans and to see the details of Microsoft Stream in the different Microsoft Office 365 Plans: https://stream.microsoft.com/en-us/pricing/. This page also explains how Stream storage works: each tenant receives 500 GB of storage and an additional 0.5 GB per licensed user, with the exception of Office 365 F1 users. Further Stream storage is available as an Add-on license.