E stands for embedded
Today sim cards are removable that contain data (SIM profile) that allows the user to access the network. If you want to change the operator that is easy just remove the old SIM and insert the new SIM card but we cannot change the data on the SIM card if u want to change the Data you need to change the SIM card itself. Now GSMA introduces a new type of technology for M2M devices they embedded a chip in all the M2M devices instead of a SIM card Slot. It allows the user to connect to the network but how do we choose the Operator and how to change the operator, we cannot use the same operator network for the lifetime. They introduce a new technology called remote improvising for remote devices Known as GSMA embedded SIM specification.
How does It work?
GSMA embedded empty chip in all M2M devices during the manufacturing of mobiles they load bootstrap in it. While switching on the mobile the bootstrap profile loads first, the bootstraps profile is like any other profile but it allows the user to connect to the first network. When the mobile switched on the chip sends a signal to the back end server somewhere to a particular operator or other controllers. This will allow consumers to download operator credentials directly to the SIM embedded in their devices, such as a tablet, wearable, or smartphone with the mobile network operators of their choice.
Example:
When the mobile is switched on for the first time the chip sends the signal to the operator. Once the operator got the request Operator sends the request to SIM vendor A to create a SIM profile for the user then the Profile will be downloaded to the chip. It will overwrite the bootstrap profile now the SIM will connect to the SIM vendor A any time. If we want to change the SIM vendor A to B choose the operator then the operator will contact the SIM vendor B and the chip will download the profile overwriting the SIM vendor A profile. 
Benefits of eSIM:
This makes life easier for people who travel abroad a lot to reduce international roaming rates. And also the user can buy a local SIM card via connecting to WIFI.
Flaws of eSIM:
In countries like India and china people use dual SIM for their convenient but this isn’t addressed by the current eSIM technology.
