Examples of an immersive app would be like a VR or AR app, and they can be used for a variety of reasons like games (Pokemon Go), training (creating a virtual environment to help trainee familiarise with the context), waypoint/guidance (e.g. for tourists or visitors).
There are other examples given, for example when I googled immersive apps/experience I saw some other examples being listed:
Mixed reality (MR) is an enhanced version of AR, tying in elements of VR as well. It often integrates entire virtual objects into the real world vs. simply adding information, with the goal of creating an even more immersive experience than AR could alone.
Digital twins are near-exact virtual models of real-life objects, processes, or systems.
360º content is a photo or a video you can “explore.” As the name suggests, 360º photos and videos are shot in every direction at the same time and let you rotate the viewing angle to see what’s “around you” as you view the video/picture.