Wall Street
In short
A narrow street in the Financial District of Lower Manhattan, New York City, that serves as the global symbol for American finance and stock markets.
In plain words
It is a real road in New York, but people use the name to talk about the entire US financial system. When news reports mention Wall Street, they usually mean the big banks and stock exchanges.
A simple example
If a news report says Wall Street is nervous about interest rates, it means investors in the global financial markets are worried.
Why it matters
It is the heart of the world's largest economy. Decisions made by the companies and banks located here affect money and jobs across the globe.
Easy to mix up
Do not confuse the physical street in Manhattan with the abstract concept of the American financial markets.