an area within an urban area characterized by ambient temperatures higher than those of the surrounding area because of the absorption of solar energy by materials like asphalt
Dome of warm polluted air which covers an urban area and in which the temperature is higher than in the surroundings. It appears as an "island" in the pattern of isotherms on a surface map.
The phenomenon of higher temperatures in a city compared to the surrounding countryside, caused by the combination of paved surfaces, lack of shade, and heat retention of buildings.