Learn in the textbookAdvancement of Mobile Communications and Device Technology
DefinitionA SIM card (SIMカード) is a small IC card that stores contract information (契約情報) such as the phone number and subscriber identity, and it goes into a device such as a smartphone.
ExplanationThe line contract is tied to the information recorded on the card. Move the card to another compatible device, and it communicates under the same contract.
AnalogyThink of a membership card: show it at the shop and the staff can tell which member you are.
Memory hookThe S stands for Subscriber, so you can read the name as "the card that tells subscribers apart".