Regio is a region of the planet Venus known as a volcanic rise. Measuring about 3000 km, it constitutes a prominent upland region of Venus centered. The first features that showed up in early radar surveys of the planet were given the names of letters of the Greek alphabet. Regio was one of those features. (wikipedia entry)
A regio is a large area marked by reflectivity or color distinctions from adjacent areas, or a broad geographic region. On Venus they are named after giantesses and Titanesses (also two Greek alphanumeric).
Image Source. Marker locations are approximate and may not always appear to align with image on map.