Numerical ones don’t seem to exist outside of IT, but other fields do the same strategy of abbreviating common long words by keeping only a letter or two. The non-numerical way is to just replace the rest with an “x” like “txn” for “transaction” in finance or “pax” for “passengers” in transportation or “sx” for “symptoms” in medicine.

Neat, that's one mystery solved. I have seen "x" used like that, but didn't know how it worked.