What is Membership 100?

In the attached screenshot with is from the Help>Customize Membership 2 page, what does "Membership 100" refer to?

Also, just confirming, the specified available custom templates for Membership 2 don't exist as individual PHP files already, right? I just create my own from scratch? I don't see any in the plugin files, but I just thought I'd ask and confirm that these files aren't hidden somewhere that I could use as a starting point.