GSM (Global System for Mobile Communications, originally Groupe SpécialMobile) 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 phones. The detail information you can learn from Wikipedia.
GSM is a kind of single, you can use device to receive it. For example, your cellphone. This document tell you how to use HackRF and Kali Linux to Sniffing GSM Traffic.
You can go to this link to learn: How to Setup HackRF on Kali Linux