Power BI Report Server is an on-premises report server with a web portal in which you display and manage reports and KPIs. Along with it come the tools to create Power BI reports, paginated reports, mobile reports, and KPIs. Your users can access those reports in different ways: viewing them in a web browser or mobile device, or as an email in their in-box.
Comparing Power BI Report Server
Power BI Report Server is similar to both SQL Server Reporting Services and the Power BI online service, but in different ways. Like the Power BI service, Power BI Report Server hosts Power BI reports (.pbix), Excel files, and paginated reports (.rdl). Like Reporting Services, Power BI Report Server is on premises. Power BI Report Server features are a superset of Reporting Services: everything you can do in Reporting Services, you can do with Power BI Report Server, along with support for Power BI reports. See Comparing Power BI Report Server and the Power BI service for details.
https://docs.microsoft.com/en-us/power-bi/report-server/get-started