What term describes a city with a population greater than ten million people?

The term that describes a city with a population greater than ten million people is "megacity." This classification is commonly used in urban studies and geography to identify particularly large urban areas that have reached this significant population threshold. Megacities often exhibit unique characteristics, such as extensive infrastructure systems, diverse economic activities, and complex social dynamics, which differ from smaller urban areas.

In contrast, a "metropolitan area" refers to a broader urban region that includes a central city and its surrounding suburbs, and it may or may not reach a population of ten million. "Urban centre" is a more generic term that can refer to any hub of activity within a city, often significantly smaller than a megacity. Lastly, a "major city" is a subjective term that can describe a city of considerable significance, but it does not specifically denote a population size and varies by context. Hence, "megacity" is the precise term to designate cities surpassing the ten million population mark.