Naming conventions in Computer Science are fuzzy and often depend on the languages which are currently en vogue. This is causing many problems because often concepts can't be mapped one-to-one

In this case:

A loop counter is sometimes also referred to as a loop iterator. A loop counter, however, only provides the traversal functionality and not the element access functionality.

There is also the term "external iterator"

IMHO the term "loop var" is the safest in a Perl context.