A cursory browse through the forum would appear to make these synonymous.
Is there a difference?
I encountered "everything buckets" (or "catchall buckets") as tools to drop stuff in directly, be it PDFs, web scrapes, images, text files, spreadsheets ... well, just everything. Then apply tags to add a level of so-called "organization" (I'm not taking this part serious, as this will break down as soon as the number of elements per tag subsets grows beyond the individual threshold of what's bearable).
A Zettelkasten is totally contrary to a bucket where you toss the original sources in and hope for the best. Much unlike any everything bucket, the note archive you use for the Zettelkasten Method should be comprised of things you wrote yourself. No web scrapings, but comments on websites. Not the PubMed PDF paper download, but notes on and excerpts of the paper.
Author at Zettelkasten.de • http://christiantietze.de/
Linking and processed thoughts(zettlekasten, deeper things I want to think about)vs raw data(everything buckets) vs notes to myself (shallow processed thoughts without linking, or nascent thoughts, or very specific technical information ). I use DEVONthink for the last two. I prefer the Archive for the first because plain text is operating system and tool indépendant.
As another example: I use Drafts as a dumping ground for anything new. It's specifically designed for this purpose, as it supports a number of "actions" to get things out to other places. I don't use any of those for ZK though, I copy and paste and edit and rewrite from Drafts into The Archive (or whatever software I'm using to manage my markdown ZK that day). Once it's in my ZK, it gets deleted from Drafts.
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