HS-open sets constitute a new class of generalized open sets introduced in the framework of bi topological spaces. This study investigates their fundamental properties and establishes their relationships with pairwise cl open sets. Several examples and counterexamples are presented to illustrate the behavior of HS-open sets and to demonstrate that certain classical topological properties are not necessarily preserved within this generalized setting. In addition, the notions of HS-open sets, HS-interior, HS-exterior, HS-boundary, and HS-closure are defined and systematically examined. Various characterizations and basic properties of these concepts are obtained, extending a number of classical topological results to the HS-framework.