[[drone war]]

What is the meaning of a post surrounded by double square brackets?

this is a [[meme]] it functions like treechat's version of a tag but can be tagged using any phrase between the brackets... it's also inspired by roam research or wikipeadia pages

And it also shows other posts with "broader" tags?
For example [[test]] meme will also show [[just testing]]
I mean memes that have my tag embedded in them?

yea they work like search query string where it ANDS the terms in the bracket