What is the difference between a primitive root mod p and a number with period p-1 mod p where p is prime?

Question

I am currently studying number theory and have come across the idea that that powers of a primitive root generate all nonzero residues in the field $\mathbb{Z}_p$ but I have also seen numbers with a period of $p-1$ in $\mathbb{Z}_p$. Aren't these the same thing? If not, how do they differ?

Apologies if my question is trivial, I am struggling to understand this concept.