noun
alt account; hidden account; sub account
Internet slang for a secondary or anonymous social media account used to post content one wouldn't share on a main account. Often implies a secret or private persona.
本アカでは言えないことを闇アカでつぶやく。
I tweet things I can't say on my main account from my alt account.
彼女は闇アカで趣味の絵を投稿している。
She posts her hobby art on a hidden account.
Compound of 闇 (yami, 'darkness') and アカ (aka, short for アカウント, 'account'). The kanji 垢 is ateji for アカ, originally from the reading of 垢 (aka, 'dirt') used phonetically in internet slang.