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鍵垢 kagiaka
A locked, private account.
What does kagiaka mean?
鍵 is a lock and 垢 is net shorthand for "account". Going 鍵垢 is how people keep a timeline to friends only — completely normal, not suspicious.
Example
鍵垢だから、フォローは承認制なんだ。
It's a private account, so follows need approval.
Vibe
Who you can say this to, and how it lands.
Safe to use Fine in ordinary conversation.
The story behind kagiaka
The 垢 in 鍵垢 is a typing joke that stuck. アカウント shortens to アカ, and if you convert アカ carelessly the machine offers 垢, a character that actually means grime. Japanese users looked at it, decided it was funny enough, and kept it. Now 本垢, 趣味垢 and 裏垢 all wear the same slightly dirty kanji.
鍵 is the lock, from the padlock on a protected account. Going 鍵垢 is completely ordinary here, and it is worth saying plainly to visitors: it does not imply anything to hide. Students, teachers, nurses and office workers all keep locked timelines so that a joke about work stays in the room it was told in.