blue cloth; blue ground; blue background
Refers to a blue-colored fabric, a blue-colored ground (as in a map or design), or a blue background. The specific meaning depends on context.
This blue cloth is perfect for a yukata.
地図の青地は海を表している。
The blue ground on the map represents the sea.
White letters stand out well against a blue background.
Compound of 青 (ao, 'blue') and 地 (ji, 'ground, base, cloth'). The reading あおじ is a standard rendaku form.