Unless you like econometrics: then X are data, betas and gammas and sigmas are unknown (oh my!).

Jargon is fun, unless I want to communicate across fields :/.

Well today I learned. I never knew that. Stupid mathematics and its inconsistent notation.

It makes sense when you look at historical development, but there is no reason to learn separate notations now without learning all sides :).

Not if you are doing econometrics/statistics.