SIM card

A smart card or embedded secure component that identifies a mobile subscriber to a cellular network and stores credentials used to authenticate network access.

International Mobile Subscriber Identity: A unique number that identifies a mobile subscription to cellular networks. The SIM stores this identifier so a network can locate the subscription during registration.
Smart card: A card containing an embedded integrated circuit that can store data and perform secure operations. A traditional SIM is a smart card designed for cellular subscriber credentials.
Embedded SIM: A soldered secure component that hosts SIM software and can be remotely provisioned with operator profiles. It replaces a removable card while preserving the SIM's subscriber-authentication role.
CDMA2000: A family of third-generation cellular standards that traditionally identified subscribers through device provisioning rather than GSM-style SIM cards. Its original provisioning model contrasted with the removable SIM approach used by GSM networks.
Authentication and Key Agreement: A cellular security procedure in which a network and subscriber authenticate each other and establish session keys. The SIM computes responses to network challenges using its secret subscriber key.
Universal Integrated Circuit Card: A secure smart-card platform that hosts applications such as USIM and SIM. The physical SIM is commonly a UICC, while SIM or USIM names the application it runs.
eSIM: A system for downloading and managing mobile operator profiles on an embedded SIM or compatible secure hardware. eSIM changes how subscriptions are installed without replacing cellular authentication itself.
Mobile network operator locking: A restriction that prevents a mobile device from accepting SIMs from some other operators. A SIM identifies a subscription, but device locking can still limit which operators it accepts.
Ki (cryptography): A secret subscriber key used to authenticate a mobile subscription to a cellular network. This key is stored securely on the SIM and is not sent over the radio link.
Subscriber identity module: A cellular application and credential set used to identify and authenticate a mobile subscription. The name SIM describes the subscriber-identity function, not strictly the card hardware.

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