Like movies, books, web-site links, videos, pictures, files
You can add ANY content type to a collection. A collection DOESN'T have to have one type of content only - like only movies or only books.
Imagine you are a sci-fi fan - and want to collect all sci-fi books, videos, movies, articles, images, so on, in ONE collection!
Let your friends and family know when you have watched a movie, or finished reading a book....and, what you thought about it!
Collections can be limited in visibility - you can keep it completely private, or share with a select few friends / family.
Optionally, you can also make your collection public! Say you are a big-shot and want to just put out there your recommended / essential reading for "Economics 101".
Let others (you shared with) also contribute to a collection - so, a collection could be a group collection instead of an individual collection!