An American Viticulture Area (AVA) is a grape-growing area with unique geographic and cultural features.
In order for a wine to carry an AVA label, at least 85% of the grapes must come from the listed AVA.
AVAs are a little confusing because there is no regional or quality-based hierarchy. Additionally, some AVAs are inside others. For example, Oakville AVA is a sub-appellation of Napa Valley AVA. And, the Napa Valley AVA is a sub-appellation within the much larger North Coast AVA.
TIP: Regions that are divided into sub-appellations tend to make higher quality wines.