PlanetPhysics/Universe of Discourse

Boole (1854) defines universe of discourse in the following manner:

In every discourse, whether of the mind conversing with its own thoughts, or of the individual in his intercourse with others, there is an assumed or expressed limit within which the subjects of its operation are confined. $$\ldots$$ Now, whatever may be the extent of the field within which all the objects of our discourse are found, that field may properly be termed the universe of discourse. (Boole 1854/1958, p. 42).