A standardized metric or statistical basket used to track the collective performance of a specific group of market assets.
Street Wall St.'s Definition:
The ultimate master scoreboard for a specific sector. Instead of checking 500 different stock tickers to see how American business is doing today, you look at one single index value to instantly get the macro vibe of the room.
Real-World Example:
The Nasdaq-100 is a tech-heavy index. When tech stocks are ripping, the index goes green. It provides a clean, standardized benchmark so investors can easily judge if their individual stock picks are actually beating the market average.