裏垢

From 裏(うら) (ura, “other side”) + 垢(あか) (aka, “account”).

裏(うら)垢(あか) • (uraaka) 

1. (Internet slang) secret personal account (on social media, especially Twitter and Instagram (finsta), as opposed to one's openly used account)
   • 2017, “イマドキの子(こ) (Imadoki no ko) [The Kids Nowadays]”, in の子(こ) (Noko) (lyrics), 幼(おさな)さを入院(にゅういん)させて (Osanasa o nyūin sasete)‎, performed by 神聖(しんせい)かまってちゃん (Shinsei kamattechan) [Shinsei Kamattechan]:

     大(おお)きな花(はな)　怨(うら)みつらみを食(た)べている
     裏垢(うらあか)に咲(さ)かしてしまうよあたしは

     ōkina hana urami tsurami o tabeteiru
     uraaka ni sakashite shimau yo atashi wa

     A large flower, eating resentment and pain
     I'll make it bloom into my other account

• Chinese:
  • ⇒ Mandarin: 裏號／里号

• リア垢(あか) (riaaka)
• 鍵垢(かぎあか) (kagiaka)