Liminal is from the natural sciences, so he was inspired by this 
They're the basis for wikis, but wikis don't have stable content, so they're actually a different thing. The content of zettel isn't supposed to vary wildly or change 5 times per day. It's something you write down and keep, to use and rearrange later, like snippets cut out of paper.
Zettelkasten - Wikipedia
