A multi-authored work, in the scholarly academic context, is typically a book written on an academic topic by academics for academics, and perhaps also practitioners and students. Of course, there are other genres of multi-authored book, for example, reference books are often written by teams of authors.
Obvious examples of multi-authored works for the scholarly environment include conference proceedings, and collections for a special occasion or person (often referred to as a Festschrift). However, to have lasting value and to be something which most scholarly publishers would want to publish, a book needs to have its own integrity and durability beyond the occasion. The subjects of the individual chapters, and their contributors, need to have been carefully selected, providing a thorough treatment of a subject with a coherent structure.
As a form of scholarly communication, the multi-authored book is less common than the journal. And that makes it difficult for someone considering becoming a volume editor to know what is involved.
Furthermore, being a multi-author book editor is not without its challenges – a book is by definition less fluid than a journal, the contents must have a logical structure and the deadline is more inexorable, so you can't delay a late submission to the next issue as you can with a journal.