An eSIM was defined by the GSMA, the membership body of all mobile operators. The abbreviation stands for Embedded SIM card, which is similar to a chip in a physical SIM but fitted in the device itself, as opposed to a removable chip. Downloading an eSIM involves acquiring an eSIM profile from secure servers with encrypted information to your mobile device.
Simply put, an embedded SIM card is the same as a normal SIM card, but not removable. A device which is ‘eSIM compatible’ contains this type of embedded card. Downloading an eSIM in reality means downloading an eSIM profile with a plan to the card embedded into your phone, through encrypted servers.