What's the term used to describe the "landing page" of a mobile app, i.e. when a user first opens the app? I know a "home page" would do for the user, but I'm looking for the technical term when communicating with a developer.
"Landing" usually means the user came from somewhere else. For example, users coming to a site through an advertisement or sent by another site. Landing pages or screens can welcome users, let them know where they are, and help them find what they're looking for.
"Launch" is usually used to describe the loading screen users first see when they "first use" the app. Apps usually have a loading time so launch screens cover over the bad experience of waiting. It's usually not interactive.
For better UX, the app should have an experience that happens when users first use the app. This is usually called "onboarding." This is where the app can show users what it can do and shows them how to get started using it.
I'm a developer and these are old popular terms. They're used by both Apple and Google. Here's onboarding in the guidelines:
I think landing page, home page or main page are widely understood. One could also use screen in place of page.
The state of the app you are referring could be named initial view, but it might very well be different state, depending on where the user comes from. (I.e. a web link, first time user, resuming previous session, etc.)
Landing page is fine. It communicates that it will be the first thing a user sees when opening the app. But you can use main screen/page if it is the place where the user will be constantly returning to.