An eSIM, or embedded SIM, is a digital SIM card embedded within a device's hardware, eliminating the need for a physical SIM card. Unlike traditional SIM cards that are physically inserted and removed, eSIMs can be remotely programmed and reprogrammed with different carriers and plans. This digital format offers greater flexibility, as users can switch between carriers and plans without having to swap physical cards, making it a versatile and convenient solution for today's connected devices.