Final answer:
The Privileges and Immunities Clause in Article IV, Section 2 of the Constitution ensures that states cannot discriminate against citizens from other states, granting them the same privileges and immunities as their own citizens.
Step-by-step explanation:
The clause in Article 4 of the U.S. Constitution that means a state cannot treat its citizens differently than citizens of other states is known as the Privileges and Immunities Clause. Specifically found in Article IV, Section 2, this clause ensures that citizens of each state are entitled to the same privileges and immunities as the citizens of whichever state they happen to be in. While it does provide for equal treatment in many respects, it does not mean there can't be any distinction in treatment between residents and non-residents, such as in-state versus out-of-state tuition at state universities or voting rights.