I found the answer to my original question in this sentence:
"77% of visitors won’t scroll; they’ll just view the content above the fold (i.e. the area of the page that is visible on the screen without scrolling down)."
http://uxdesign.smash...ndings-and-guidelines
Now that I've found the term "above the fold", I can decide whether or not it is too technical for my audience. For example, if I am going to talk about it a lot, I might explain it the first time I use it, like the author did in that article.
The article goes on to say that users' habits have changed and that (because of the variety of available display resolutions, as Rojash said) "above the fold" has become a somewhat outdated term. However, I still think it's a good idea to have the core essentials "above the fold". I can think of plenty of websites that have too much "below the fold". For example, I find the landing page of the Daily Mail website very heavy.
And there, in my last sentence are two items of vocabulary which would not be understood by many audiences ("heavy" and "landing page"). I'm confident though that they'll be understood by the readers of this thread (there's another word, "thread").