AKB48 is a highly successful Japanese pop group which was formed by Yasushi Akimoto in 2005 and has expanded into an international franchise.
The AKB48 franchise include its Tokyo based main group, and sister groups SKE48 (Nagoya based), SDN48 (adult group), NMB48 (Osaka based), HKT48 (Fukuoka based), JKT48 (Jakarta, first international franchise), and SNH48 (Shanghai based).
There’s also Nogizaka46, which is labelled as a “rival group” of AKB48 but is part of the franchise nonetheless.