Embedded Subscriber Identity Module is a chip that is soldered on the motherboard of your phone. This chip can be programmed with the selected carrier’s profile usually by using a QR-Code, or the carrier’s app. Since eSIM is embedded into the phone, you can’t just take it out, and place it into another phone. However, with most people keeping their phone for a couple+ years, this is not much of an issue. For those that changes phones frequently might have more of an issue, and there are a select number of phones that are eSIM only, therefore removing the choice of using a SIM card.