The AK-47 is a selective-fire, gas-operated 7.62×39mm assault rifle, first developed in the USSR by Mikhail Kalashnikov.
Officially known as Avtomat Kalashnikova (Russian: Автомат Калашникова), it is also known as a 'Kalashnikov,' an "AK".
The ingame model in CS:GO is actually a AKM, an upgraded version of the AK-47 developed in the 1950's. The AK has been a staple of the CS series since it's inception in the late 90s and is always represented as a powerful assault rifle with exceptional first shot accuracy, high recoil, and one-shot kill potential. Being the workhorse of insurgent forces it is only available for purchase by the Terrorists, with Counter-Terrorists being able to acquire one only by looting dead terrorists. (Full article...)