hiding one's mistakes; covering up wrongdoings
Refers to the act of concealing one's errors, misdeeds, or embarrassing facts. Often used in contexts of personal or professional cover-ups.
He tried to cover up his own mistake.
The politician's cover-up came to light.
back pocket
Literally the back pocket of trousers or a skirt. This sense is less common and may be considered a literal or slangy extension of the 'hiding' meaning.
He put his wallet in his back pocket.
Compound of 尻 (shiri, 'buttocks, rear') and 隠し (kakushi, 'hiding'). The literal meaning 'hiding the buttocks' gave rise to the figurative sense of concealing one's faults, and by extension the back pocket where items are hidden.