Looking for the definition of a specific group: $C_p$

Question

I saw an exercice that asked me the following:

"Show that if $G$ does not have any non-trivial subgroups than there exists a prime $p$ such that: $G \cong C_p$"

Now my problem is: I don't know what the group $C_p$ is. Our professor did not define it and I didn't find a definition on the internet

Answer 1

It's the cyclic group of order $p$, a.k.a. $\mathbb{Z}_p$ or $\mathbb{Z}/p\mathbb{Z}$ or "the integers modulo $p$".