Issuer Security Domain (ISD)
An issuer security domain is a protected area on a smart card or eUICC that controls the loading and management of applications or profiles.
What is Issuer Security Domain (ISD)?
On an eUICC, the ISD-R (root) is the single domain that manages profiles and talks to the LPA, while each downloaded profile sits in its own ISD-P, isolated from the others. The concept comes from the GlobalPlatform card specifications.