Before the OS can orchestrate one, the word has to mean something. Here's what it means — in plain terms first, then in the register the system reasons in.
An experience is something you choose to do, somewhere specific, that takes up real time, feels different depending on where and how — and leaves something behind in you.
It composes the whole experience — held end to end, paced to your arc, adapting when reality shifts, remembered for the next.