What is the term for a Tumblr blog that has multiple contributors?

A Tumblr blog with multiple contributors is called a group blog.

Tumblr’s group-blog feature lets several users contribute to the same secondary blog. Members can publish posts, while administrators have additional powers, such as inviting or removing members and deleting posts made by others.

A group blog is not the same thing as a group chat or a general collaborative project. “Team blog,” “collaborative blog,” and “multi-author blog” are understandable descriptions, but “group blog” is Tumblr’s official term and the canonical quiz answer.

There is an important Tumblr-specific detail: only secondary blogs can become group blogs, and only users’ primary blogs can join them. Group blogs also have limitations, including no private messaging. Tumblr introduced this structure to let communities, fan groups, organizations, and creative teams publish under one shared identity.