Interfaces are the regions where distinct phases meet and the symmetry of bulk matter is broken, generating excess free energy that influences structure of matter, its stability, and function across scales. In this work we identify, three closely related quantities: interfacial energy γ, interfacial structure or coverage φ, and spatial gradients in interfacial energy ∇ₛγ that can strongly influence the performance of the materials and devices in various fields, such as materials science, nanotechnology, integrated circuits, chemistry and engineering. Moreover, we show how these three quantities can help us interpret diverse phenomena, including friction and adhesion, superhydrophobicity and omniphobicity, nanoparticle self-assembly and propulsion, thin-film processing in photolithography, detergency, emulsion and foam stability, multiphase flow in enhanced oil recovery, or atmospheric water harvesting. Because these three quantities are interdependent, they establish a solid triangular base for understanding and discussing equilibrium thermodynamics, kinetic stability, non-equilibrium transport, and engineered multiphase systems. We offer this as a conceptual framework, not a complete theory, that specialists and newcomers can use to compare interfacial problems across fields and to connect them to technological applications.