Many peculiar EM modes revealed in photonic/plasmonic metastructures have greatly enriched the research of modern optics, electromagnetics, and photonics, and have been increasingly inspiring many advanced applications in both classic and quantum regimes. These modes include, for example, surface plasmon polaritons (SPPs), localized surface plasmon (LSPs), and their counterparts in lower frequencies etc. Conventionally, much attention has been paid to exploring the physical properties of these modes. Very recently, their geometric properties or topological features have increasingly gained interest since the nontrivially topological features (e.g., phase and polarization singularities, or other topological defects like optical skyrmions) bring many fascinating properties for these modes, e.g., topological protection and orbital angular momentum (OAM), etc. This session focuses on both the physical and geometric properties of these peculiar modes and their applications at microwaves or higher frequencies. Example topics include microwave devices, antenna and propagation, EM transmission enhancement, and EM absorption based on these peculiar EM modes, and also include OAM beams, EM/optical polarization vortices, and optical skyrmions, etc.