Refers to food supplies, especially for military, expeditions, or emergency use. Somewhat formal or technical.
The soldiers marched carrying three days' rations on their backs.
The disaster victims survived for a week on meager provisions.
Compound of 口 (mouth/eating) and 糧 (provisions/food). The exact historical derivation is uncertain, but the combination naturally conveys 'food for the mouth' or 'edible provisions'.