Confidential Talk, Whispering
noun
The inside together talk is talk that's only inside between us. It's confidential talk.
ないしょばなし
This word uses the on'yomi of 内緒 and kun'yomi of 話, only rendakued.
当人達は内緒話をしているつもりのようだが、声がでかいので全部筒抜けだよ。
They are trying to whisper to each other, but their voices are so loud that I can hear everything.