There are at several possible ways, actually.
First is to avoid the yet-to-be-defined term in the intro and use a descriptive phrase instead. This assumes the term isn't frequently used in the intro.
A second way is to footnote the definition or an pointer to it when it first appears in the introduction. Putting the definition itself in the footnote repeats it, but a pointer doesn't require that.
You could also just add "... frytopper (defined in the next section)..." at the first appearance.
Yet another would be to write the intro as: "... frytopper (italicized terms defined in the next section)...". For this you would only need the pointing phrase at the first of the later-defined terms, but just italicize all of them - at least for the first appearance.
Some of these require the reader to hop about a bit, but it should work.