erd – Domain of Attributes for an Entity?

I am new to DBMS and was reading about the ER Model and entities-attributes. I found the following line in the book which I was reading:

The domain of Composite attributes is the cross product of domains of
component attributes.

Which is fairly straight forward and intuitive. However, I was not able to understand the line following it:

The domain of Multi-valued attributes is a set of subsets of values
from the basic domain.

I couldn’t understand this line. I know Power set, which is set of all subsets of a set. Does this line mean, The domain is the power set of the basic domain set? I tried searching on the web before posting, but couldn’t find any related literature/ explanation.

A simple language explanation would help! Thank you!