What does the item symbol of a document with two people mean?

gwtw14
I have a pdf item in Zotero with a symbol of a paper with a folded upper right corner and two people (in green and blue) in the front. (Sorry, I would post a screen shot but I can't add images in this forum..)
What does this mean? I would assume it should signify some sort of sharing, but I haven't done anything (intentionally) like that on Zotero.
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