CUSTOMER TERMS
What does it mean when terms are listed as 10% prox? (what does prox mean)
What does it mean when terms are listed as 10% prox? (what does prox mean)

Where are you seeing this? Is this on an invoice from a vendor to you?
Prox terms are terms that were used by companies that issued many invoices to one company in the days before computers. I managed a masonry supply company in the '90's that used prox terms and now I deal with electrical materials supplies that still use prox terms. These terms seem to be used by building materials suppliers.
Generally, the terms would be something like 2% 10, net 30 prox. With that scenario, all purchases made the previous month would be eligible for a 2% discount if paid by the 10th day of the following month and if you did not take the discount, all your invoices from the following month would be due on the 30th.
Your example is a bit brief. I would expect a little bit more description than what you are seeing. I would call your vendor for a better explanation. That said, prox generally means that your bills are due at the end of the following month.