The history of the term "Above the fold" comes from newspapers where the articles at the top were most visible when the newspaper was folded. To quote this Wikipedia article
Above the fold is the upper half of the front page of a newspaper
where an important news story or photograph is often located. Papers
are often displayed to customers folded so that only the top half of
the front page is visible. Thus, an item that is "above the fold" may
be one that the editors feel will entice people to buy the paper.
Alternatively, it reflects a decision, on the part of the editors,
that the article is one of the day's most important. By extension, the
space above the fold is also preferred by advertisers, since it is the
most prominent and visible even when the newspaper is on stands.
With regards to developers, while most developers I work with understand the above the fold term, if users or stakeholders dont understand, I explain it as the content that is visible when you first load a page and what you can see without scrolling.
However do note, above the fold is a relative term as it depends upon the resolution and the form factor of the device used to view the content.
I also recommend reading this witty article about the fold