Are event and mode well defined terms in CS literature? From my experience in programming small imperative scrips for personal usage with JavaScript,
I can conclude that an event is "A perceived change in the output of a system" (such as clicking a link from client side or refreshing a page from server side),
while a mode is a situation or "state of affairs" of a program (such as a "saved game" state we can later "load") and if a certain state has happened the program can behave in some way (such as terminating itself).

But if at all, are event and mode well defined terms in CS literature and if so, what is the difference between them?
I'm not sure whether they have accepted meanings, but to the extent that they do, an "event" happens at an instantaneous point in time, as opposed to something ongoing.  If I was reading something that used the word "mode", I probably wouldn't be sure what is meant by "mode" without looking at the context.

I'm not sure whether you should expect precise, widely-accepted definitions for terms that are used informally.