What does Amazon consider business days?

I’ve just started listed a few of my old books and a few neat old books I found at a yard sale for 50 cents each on Amazon’s marketplace.
Most of the rules for sellers make sense of some kind, no problem there.
One line states,
“You have agreed to ship no later than two business days after the
buyer’s purchase on XX-XX-XXXX.”
What are business days?
Are they Monday-Friday?
Are they Monday-Saturday?
If Monday is a federal holiday, does it count?

Okay, and I reread my post.
One could reach the conclusion that I was listing my items for 50 cents each.
I am listing no items for less than $5 because without a “Power Seller” account the commissions on anything below $5 would eat me alive.
I mentioned 50 cents to say that it was the price I paid, for example, for a 1941 printing of “Aristophanes: The Eleven Comedies”.

Normally, business days are Monday-Friday, excluding holidays. (Holidays are usually days when federal services shut down, although I assume that also includes different holidays that are observed only by certain states, in that state.)

M-F minus holidays. If the post office isn’t open that day, it dosen’t count.

Thanks to both of you!