In trading, the individual assets aren’t the only ones used for trading. There are other asset types like indices, ETFs, etc. Indices, for example, are a collection of individual assets that generalize their prices and offer the average value.
The most popular indices can be found in stock trading, but there are also currency indices Forex traders use. As you may know, stocks are the shares of the companies, therefore, the stock indices combine the companies and their values. If the companies are doing great, the index value increases as well; and if they’re unsuccessful, the index value declines.