The expression $(A \cup B \cup C)'$ represents the complement of the union of sets $A$, $B$, and $C$. To break it down:

1. Union: The union $A \cup B \cup C$ represents all elements that are in $A$, $B$, or $C$ (or any combination of these sets).

2. Complement: The complement of the union $(A \cup B \cup C)'$ includes all elements that are not in the union. In other words, it consists of elements that do not belong to any of the sets $A$, $B$, or $C$.

If you are working within a universal set $U$, the result is:

$(A \cup B \cup C)' = U - (A \cup B \cup C)$

This is the set of all elements in the universal set that are not in $A$, $B$, or $C$.

Would you like more details or examples on this? Here are some related questions:

1. What is the result of $(A \cup B)'$ in set theory?
2. How is the intersection of sets $(A \cap B)'$ handled?
3. What is the complement of the intersection $(A \cap B \cap C)'$?
4. Can you explain De Morgan's laws for set operations?
5. How do you find the symmetric difference between two sets?

Tip: In set theory, the complement refers to elements outside the set, often within a defined universal set.