Short definition
Wine made entirely from grapes grown on the winery's own vineyards and bottled on the property.
Estate bottled means one operation grew the grapes, made the wine, and put it in the bottle. No purchased fruit, no outsourced winemaking. In the US, the winery must own or control the vineyards in the same appellation. The French equivalent is "mis en bouteille au domaine." It is not a guarantee of quality, but it does mean traceability and consistent intent.