Power Platform is a software suite that includes business intelligence, app development, and app connection. The Power Fx low-code programming language was created by Microsoft to convey logic across the Power Platform.
Microsoft's Power BI is an interactive data visualization software application that focuses on business intelligence. It is a component of Microsoft's Power Platform.
Power Applications is a collection of apps, services, and connectors, as well as a data platform, that allows you to quickly create unique apps for your organization.