Stock Indices are groups of stocks that represent part of the financial market and track the performance of a group of stocks. For example, the S&P 500 follows the stocks of 500 large US companies. When people refer to 'market' performance in stock index trading, they often mean how major indices like the S&P 500 are doing. Traders can buy and sell instruments that track indices, speculating whether an index will rise or fall.
How stock indices work:
Indices are weighted to reflect the size and price of the stocks within it.
In the S&P 500, larger companies have more influence based on their total market value. This is called market capitalisation weighting.
In the FTSE 100, stocks are weighted purely by their share price. Expensive stocks carry more weight.
Instead of picking individual stocks, traders can use indices to invest in many stocks at once. Index performance reflects overall market trends.
There are also exchange-traded funds (ETFs) that mimic indices. ETFs provide a simple way to gain broad index exposure without buying all the stocks directly.