Urban heat island is a metropolitan area that is significantly warmer than its surrounding rural areas due to human activities and altered land surfaces. As an academic concept and research field, it systematically investigates the physical processes, anthropogenic factors, and landscape characteristics (such as reduced vegetation, impervious surfaces, and building morphology) that contribute to this thermal differential. This concept is crucial for understanding the environmental, health, and socio-economic impacts of urbanisation, including effects on energy consumption, air quality, human comfort, and biodiversity.