An web browser. 99 percent of my mobile activities are done in Firefox. I have Organic Maps for routing, a local mobile payment app and a local sharing electric sooter app.
I understand your point. "Program" is a more wider term. Javascript executed in your browser could be a program too. App is just a short term for a standalone program with a GUI, IMO.
It's just how languages change with time. For example what we simply call "libs" today used to be called by their full name "program libraries". You don't often see someone calling them like that anymore. I feel that communication nowadays requires us to constantly check the context in order to avoid misunderstandings. It's maybe a reason why I don't write that much online anymore.