I was using my own wording for the distinction.

But sorry "plain variable" is blah.

The fact that other languages do implicit dereferencation in their syntax doesn't make them less plain.

$a, %a and @a are in fact containers for references, to allow such implicit dereferencation. °

So how are containers "plain" now?

But Perl is more explicit* here, which helps understanding what is really happening if you do an assignment a=b in another languages, where they sometimes copy the content or the reference.

updates

°) e.g. $a[0] is by definition (\@a)->[0]

*) "Explicit is better than implicit" quote from Python blah