Nogizaka46 is a Japanese female idol group produced by Yasushi Akimoto, and it is billed as the "official rival" (公式ライバル kōshiki raibaru) of the group AKB48.

Nogizaka46 was named after the place where the SME Nogizaka Building, which houses Sony Music Japan’s office, is located in. Their producer Yasushi Akimoto also said that the number "46" was chosen as a direct challenge to AKB48.

(Source: Wikipedia)