The Avtomat Kalashnikova series of rifles are rifles that have seen production since 1947. Since the original AK (in the US, it's known as the AK-47), there have been different variants/ improvements made as the years go on. The AK series of rifles are also Russia's current standard issue rifles, in both the military and some law enforcement branches. The design of the AK is also rather influential, many Russian rifles since the AK having similar attributes.
In Escape From Tarkov, the AK-74 assault rifle is the standard issue rifle of BEAR operatives. The AK-47, AK-12 and other variants are also likely to be present in the game.