An eSIM, or embedded Subscriber Identity Module, is a virtual SIM card integrated into devices like smartphones and smartwatches. Unlike physical SIM cards, eSIMs are programmed remotely, enabling easy network switching and activation without needing physical swaps. They offer flexibility for changing carriers and plans, convenient international travel connectivity, and the management of multiple numbers on one device. While not universally supported, eSIM technology reduces the reliance on physical cards and simplifies the user experience by allowing remote provisioning of cellular services.