Melissa Coates gives us the different forms of what an “app” is in the Power BI world:
Let’s say you just heard someone mention a Power BI app. What exactly do they mean by that? Well, it depends. The term “app” is used kind of a lot in the Power BI world. So, here’s a quick reference to help you decode the conversation. I’m going to start with the most likely options, working down to other options. Which one someone is referring to really depends on their role and their level of familiarity with the Power BI ecosystem.
Power BI App
A Power BI App is a packaged up set of content in the web-based Power BI Service. Related reports, workbooks, dashboards, and datasets are published from an App Workspace into an App for users to consume.
Power BI App Workspace
An App Workspace in the Power BI Service is where reports, workbooks, dashboards, and datasets are saved, and where data refresh schedules and other settings are defined. An App Workspace is suited to development & collaboration with coworkers (whereas My Workspace is a private area). Smaller teams might do everything they need to do within an App Workspace, whereas larger teams use an App Workspace as the collaboration area for content before it gets published to a Power BI App for consumption. You can have quite a few App Workspaces, depending on how you organize content (for instance, by subject area, by project, by department, or by type of analysis).
Click through for several other potential answers for what that user means by “app.”