Learn in the textbookAdvanced Authentication Methods and Payment Authentication
DefinitionSMS authentication (SMS認証) sends a one-time verification code by SMS (text message) to a registered mobile number and confirms identity when the user types that code in.
ExplanationOnly someone holding the device for that phone number can receive the code, so having the device becomes the proof of identity. Combined with a password, which is a knowledge factor, it gives multi-factor authentication (多要素認証), stacking factors of different kinds.
AnalogyIt resembles a parcel locker whose pickup code goes only to the recipient's smartphone: only the person holding that phone can read the number.
Memory hookSMS stands for Short Message Service: short texts addressed by phone number alone, so holding the receiving device is the evidence.