Refers to strength of character, the courage to stand by one's principles, and resilience in the face of difficulty. Often used in formal or literary contexts.
He is a politician with backbone.
Even when facing hardship, I won't lose my grit.
strong moral fiber; backbone; unyielding spirit
Compound of 気 (spirit, mind) and 骨 (bone), literally 'spirit-bone', suggesting an inner framework of moral strength. The exact historical derivation is uncertain, but the metaphor is transparent.