"Database Only" collections don't have titles, but a link appears for them in your WorldCat Discovery A-Z Collections list (found at [yourlibrary].on.worldcat.org/atoztitles/browse/collections).
Database-only collections are used primarily by WorldShare Acquisitions and WorldShare License Manager libraries when they need to acquire collections or associate licenses with collections that do not have a defined list of titles. For example, a library might create a database-only collection for the Oxford English Dictionary website.
Doing so would:
Note: Database-only collections will not set holdings in WorldCat or output MARC records.