Definition
A stock index is a basket of stocks representing a specific market, country or sector. The index is calculated as a weighted average price of the stocks in the basket and used as a benchmark for market performance.
Important indices
OBX — Oslo Stock Exchange top 25 · S&P 500 — USA 500 largest · Nasdaq 100 — US technology · MSCI World — global
Benchmark: Indices are used to measure whether your portfolio performs better or worse than the market. Beating the index over time means you are a good investor.
"The benchmark determines whether you win. Know the index — and always know where you stand relative to it."— Florence Scovel Shinn