TITLE: What is the meaning of $(\mathbb{Z}/ n \mathbb{Z})^{\times}$?
QUESTION [5 upvotes]: As the notation of Multiplicative group of integers modulo n I see: $(\mathbb{Z}/n \mathbb{Z})^{\times}$
What does this notation actually mean?

REPLY [2 votes]: $n\mathbb Z$ is the set of integers that are multiples of $n$
$\mathbb Z /n\mathbb Z$ is the "Quotient group."
It is the set of remainders when we choose an integer and subtract members of $n\mathbb Z$
You might know it as integers mod n.
And you might also see it as $\mathbb Z_n.$  If nothing is said about the group operation, assume it is addition.  But it really is better to be explicit about those things.  $\mathbb Z_n^+$
$\mathbb Z / n\mathbb Z^\times$ or $\mathbb Z_n^\times$ would be a group of integers mod n with the operation of multiplication.