Final answer:
The 'wall of separation' between church and state refers to the Establishment Clause of the First Amendment, which prevents the government from establishing a state-sponsored religion or showing favoritism among religions.
Step-by-step explanation:
The "wall of separation" between church and state is most closely related to the Establishment Clause of the First Amendment to the US Constitution. The Establishment Clause is known for prohibiting the government from establishing a state-sponsored religion and is often interpreted as ensuring there is no favoritism of some religious beliefs over others or religion over non-religion. This clause is central to the concept of separation between religion and government in America.