What is $\mathbb{Z}^*_p$?

Question

What is $\mathbb{Z}^*_p$ ?

I think $\mathbb{Z}_p$ is the ring of p-adic integers but not sure what the * represents.

Answer 1

The star usually refers to the group of units of a ring $R$. Another notation is $U(R)$.

Answer 2

It's the group of $ p $-adic units.