Aliasing is the phenomenon where two different expressions actually refer
to the same thing. Modifying one will modify the other, and if you take a
reference to both, the two values are the same.

Aliasing occurs in Perl for example in for-loops and sub-calls:

for $var ($x) {
# here $var is an alias to $x
}

foo($y);
sub foo {
# here $_[0] is an alias to $y
}

Data::Alias is a module that allows you to apply "aliasing semantics" to a
section of code, causing aliases to be made whereever Perl would normally
make copies instead. You can use this to improve efficiency and
readability, when compared to using references.

The exact details of aliasing semantics are below under the /DETAILS
manpage.