Some applications live in a single process, while others span processes and machines. There are clear differences, but also enough in common to speak of “APIs” for both
Just as I am irritated that people seem to have forgotten that "applications" can potentially run completely locally, and that programs can be designed around the assumption that the "front end" (UI) and "back end" (business logic) will communicate directly (or at least exist within the same process, even if there are good reasons to set up message queues etc.).
But, you know, that's bad for business. Because that entails that the consumer might actually get to own something, even if it's just an ephemeral pattern of bits on local storage.