inside story; inside information
Refers to confidential or behind-the-scenes details, often about an event, organization, or decision-making process.
The reporter got the inside story on the incident.
He knows the inside details of the company thoroughly.
Compound of 内幕 (uchimaku, 'inside curtain' → 'inside circumstances') and 話 (banashi, 'story'). The exact historical derivation is uncertain, but the word is conventionally associated with revealing hidden details.