Full Idea
A 'free' logic is one in which names are permitted to be empty. A 'universally free' logic is one in which the domain of an interpretation may also be empty.
Gist of Idea
A 'free' logic can have empty names, and a 'universally free' logic can have empty domains
Source
David Bostock (Intermediate Logic [1997], 8.6)
Book Reference
Bostock,David: 'Intermediate Logic' [OUP 1997], p.360