What is the name of an element in a poset that divides it to two posets?

Question

If I have a partially ordered set $P$, I am wondering what do I call an element, $n$ that divides $P$ to two subsets $S,R$ such that $\forall s\in S, s<n$ and $\forall r \in R, r>n$.

In other words, thinking of the partial order as a DAG, its a point that has to be in a fixed position in a topological sort regardless of which topological sort it is.

Edit: Example, vertex 3 here represent the node I am thinking about:

Answer 1

To use a term from topology, it is a cut point.