You cannot exactly say always what is junk and what not.
There are a lot of things like binary plains, file paths, etc. which are surely junk because they are not genuine passwords.
Here on Hashes.org junk means something like non-genuine-passwords and there are people working on finding such plains by regex or other methods to filter them out to get a clean found.txt list which contains as much as possible real good passwords. By this definition random passwords also are considered as junk.