Is a Junction-Table basically just the table that sits between two entities that have a M-M relationship?
A junction table is a weak entity, but a weak entity often is not a junction table. A junction table is not the same as a weak entity. A junction table is a type of weak entity.
Tables used to resolve repeating groups are also weak entities. These are only junction tables if the repeating group contains a repeated foreign key relationship.
Depends how you define a "junction table". ER terminology tends to be somewhat ambiguous when used to describe relational database concepts.
A junction table typically means or can mean any table with two or more foreign keys.
A weak entity on the other hand is represented by a table whose primary key includes at least one foreign key attribute. That doesn't have to be the case for a junction table (i.e. a table with more than one foreign key).