Global System for Mobile Communications (GSM)

A digital cellular phone technology (standard) first deployed in 1992. GSM
uses narrowband TDMA, which allows eight simultaneous calls on the same radio frequency .

The Global System for Mobile Communications (GSM) is a standard developed by the European Telecommunications Standards Institute (ETSI) to describe the protocols for second-generation (2G) digital cellular networks used by mobile devices such as mobile phones and tablets .

Sources:

Dictionary of Computer and Internet Terms (Vol. 1) John C. Rigdon, 2016 – 1471 c. – 568

Martin Sauter (23 June 2014). From GSM to LTE-Advanced : An Introduction to Mobile Networks and Mobile Broadband (Second ed.). John Wiley & Sons, Incorporated. ISBN 9781118861929.