What does the universal set symbol represent?

The universal set symbol represents the entirety of the elements being considered in a particular discussion or context. In set theory, when using a Venn diagram, the universal set is typically represented by a rectangle that encapsulates all other relevant sets. Everything inside this rectangle constitutes the universal set, meaning it includes all elements under consideration, whether they belong to a specific set or not.

This context is critical when dealing with operations in set theory, such as unions, intersections, and complements, as it defines the boundary of what is included in the discussion about sets. The other options do not accurately represent the function of the universal set symbol: it does not denote just elements of a specific set, nor does it refer specifically to intersections or elements outside of any sets.