The technical term for 5.56 and similar rounds is intermediate cartridge and includes 7.62×39mm, 5.56×45mm NATO, 5.45×39mm & 7.62x35mm among other cartridges. The definite from wiki is 'An intermediate cartridge is a rifle/carbine cartridge that is shorter than typical full-power battle rifle cartridges, but still has greater length than pistol/personal defense weapon cartridges.'

https://en.wikipedia.org/wiki/Intermediate_cartridge