Correct terminology: Can I use the term "unknown/s a priori"?

Question

I am trying to solve a regularized least square problem which has two regularization constants: muT, muS. Further, my solution also needs underlying B1-error (MRI terminology) estimation and then subsequent correction. Unlike, muT, muS, B1-error is an experimentally measurable quantity; but, we only need it for some correction.

Questions: 1) What is the meaning of unknown a priori? Can I say that B1-map is unknown a priori?

2) Is it okay to say muT and muS are unknowns a priori? (notice that I used plural "unknowns".

Answer 1

1. It presumably means unknown before you see the data, but without context, it may be hard to know what someone means when they say it.

2. In English you'd normally say $\mu_S$ and $\mu_T$ are unknown a priori.

   You're not calling them unknowns in that expression, you're saying you don't know them. If you wanted to refer to them as unknowns, why would it matter whether it was a priori or not? You don't know population parameters after you see the data either.