eUICC (embedded Universal Integrated Circuit Card)
Updated
An eUICC is a SIM that can store several operator profiles and receive new ones remotely, over the air, instead of being replaced physically. The way profiles are downloaded and managed is specified by the GSMA: SGP.02 for machine-to-machine, SGP.22 for consumer devices and SGP.32 for IoT.
In practice
With an eUICC, a device deployed in the field can change mobile operator without anyone touching it, which protects long-lived products against network shutdowns and permanent roaming rules.