What does 内緒 mean?
内緒 is a Japanese noun meaning “secrecy, privacy, secret” in English. It can also be translated as “one's circumstances (esp. fiscal), inner realization, kitchen” depending on context. It is written as 内緒 in kanji, ないしょ in hiragana, and naisho in romaji. This word is part of JLPT N1 vocabulary.
Example sentence
彼女は内緒で私にその話をした。
She told me the story in confidence.