Fetching details from the dictionary...

secrecy; confidentiality; privacy; secret
one's circumstances (esp. fiscal)
inner realization; personal enlightenment
kitchen
このことは内緒にしておいてほしいんだけどいい?
I want you to keep this a secret, okay?
彼女は親に内緒でアルバイトを始めたらしいよ。
She apparently started a part-time job without telling her parents.
内緒の話があるんだけど二人だけで話せないかな。
I have something confidential to tell you - can we talk alone?