The discussion centers around the concept of an open subset in R^n and its relationship to functions. It clarifies that a function u maps elements from an open subset U to real numbers, indicating that U is a subset of another set P. The key point is that for every element x in U, it must also belong to P. The participants seek to understand the implications of being an element of an open set in R^n. Overall, the conversation emphasizes the nature of functions and subsets in mathematical contexts.