What is the difference between the normal distributions weve seen in previous chapters and (a) a z-distribution

Question:

What is the difference between the normal distributions we’ve seen in previous chapters and
(a) a z-distribution and
(b) a sampling of means?
Distribution
The word "distribution" has several meanings in the financial world, most of them pertaining to the payment of assets from a fund, account, or individual security to an investor or beneficiary. Retirement account distributions are among the most...