Most categories are self-describing. However, three need explanation.

100Unknown

David N. Meyer wrote a book “The 100 Best Films To Rent You’ve Never Heard Of”. Any film from this book is in the category “100Unknown”.

1000NYTimes

The film critics of the New York Times have compiled “The New York Times Guide to the Best 1000 Movies Ever Made”. Any film from this book is in the category “1000NYTimes”

1001BeforeDie

Steven Jay Schneider is the general editor for the 5th anniversary edition of “1001 Movies You Must See Before You Die”. Any film from this book is in the category “1001Before Die”.

Of course any film can be in several categories. Indeed, there are films that appear in more than one of the above 3 categories. In fact, it seems to me that for a film to appear in more than one collection is a sort of vote of confidence.