Abbreviations: IOU and JIT

Hi, in an English level assessment test I have come across these two abbreviations:
JIT and IOU. I hadn’t seen them before, according to acronymfinder they can mean ‘Just In Time’ and ‘I Owe You’. (there are many other possible meanings). Now, my question is how common are those two abbreviations in business? I mean, acronyms or abbreviations like a.s.a.p. and CEO or often used in business correspondence. I’m not so sure about JIT and IOU though.
Thanks in advance. As ever.

PS: Is there a difference between thanks in advance and thanks beforehand?

Hello Jamie (K)! Your explanations are very interesting, thank you for sharing your knowledge with us. Incidentally, I’ve checked the word promisory note and it occurs that it spelled like with two s: promissory note.

Yes, I thought of that after I hit “submit”. So, you see that even native speakers get confused about spelling. In English legal language, we have the words promisor and promissory. It’s not easy to keep track of.