Short answers, pulled from the story.
A central business district, or CBD, is the commercial and business center of a city. It contains commercial space and offices, and in larger cities is often described as a financial district. It is usually highly accessible with a large concentration of specialised goods and services.
Not always. A CBD often coincides with the city centre or downtown, but many cities have a central business district located away from their traditional city center. A single urban area can also contain multiple CBDs, and downtown sections, especially in North America, are often distinct from CBDs and city centres.
La Défense, west of Paris, is France's largest central business district, and as of 2025 it was Europe's largest purpose built business district. It hosts 19 of the world's biggest 500 companies, while the Paris region as a whole hosts 29 of the world's 500 largest companies.
Cities with strong preservation laws and maximum building height restrictions, meant to retain the character of the historic and cultural core, often place their CBD far from the city centre, sometimes outside the city limits. This pattern is common in European cities such as London, Paris, Moscow, Vienna, Prague and Budapest.
In the 21st century, increasing urbanisation has led to megacities that often have multiple CBDs scattered across the urban area. São Paulo is described as a multipolar city with several business districts, and Seoul includes three central business districts: Downtown Seoul, Gangnam District, and Yeouido.
The City of London and Canary Wharf serve as the United Kingdom's largest CBDs by economic output, and the City holds the vastest concentration of economic output in the world. In the 2023 Fortune 500 Europe list, London had 44 companies, about 9% of the list's revenue.