noun
A somewhat literary or poetic term for a battlefield, literally 'garden of battle'. Not the most common everyday word for battlefield (that would be 戦場).
彼は戦いの庭で勇敢に戦った。
He fought bravely on the battlefield.
The standard, neutral word for 'battlefield'. 戦いの庭 is more literary and less common.
Compound of 戦い (tatakai, 'battle') + の (no, possessive particle) + 庭 (niwa, 'garden'). The exact origin is uncertain, but it is a poetic metaphor for a place of battle.