“Fill-in-the-clue” clues have blanks in the clue that the answer fills in. It’s similar to fill-in-the-blanks, but the answer’s letters can be split up and can also appear partway through other words. Here’s an example:
“Mer_ury or S_tu_n”
If you fill in the clue, you get “car”, which is a possible answer for “Mercury or Saturn”.
You not only gain more letters of the answer from getting a crossing word, you get more letters of the clue!
Enjoy! (it’ll make more sense once you get going)