The chip inside the phone that stores one or more eSIM profiles.
eUICC stands for embedded universal integrated circuit card. It is the built-in chip that holds eSIM profiles, in the same way a plastic SIM holds one profile on a removable card.
You rarely see the term on a plan page. It appears in phone specifications and in help articles that explain why an older phone cannot take an eSIM.
What to check
- If your phone settings show an EID, the phone has an eUICC
- Phones without an eUICC cannot install a travel eSIM