The AKMSU is a compact carbine version of the Soviet AKM assault rifle. AKMSU stands for Assault rifle ('Automat' in Russian) by Kalashnikov, Modified, Skladivaushiisya (folding-stock), Ukorochenniy (Shortened) - Soviet assault carbine. It is frequently called "AK74u", which is actually a similar weapon but caliber differences and newer building technics (the AKS-74U) but is based on the AK-74

AK-74

The AK-74 is an assault rifle developed in the early 1970s in the Soviet Union as the replacement for the earlier AKM...

rather than the AKM.