Create and join research groups to focus on any topic you choose. Each group can share its own research library, complete with files, bibliographic data, notes, and discussion threads. Tag and analyze your research together with others. Work with a single colleague or an entire class: Zotero groups can include as many members as you please.
Zotero's Groups feature allows you to share references with other Zotero users online. It's a great way to work on collaborative research projects.
From Georgia State University Library:
You now have two sections in your Zotero collections pane: My Library and Group Libraries.
Personal and group libraries are entirely separate, and changes made to items in one library do not affect the other. You can drag items back and forth libraries to copy items.