The term ‘index’ can refer to several concepts across different fields, but generally, it denotes an indicator or measure of something. In the context of publishing, an index is a list typically found at the end of a book that provides references to the pages where specific topics, terms, or names are mentioned, allowing readers to locate information quickly. In finance, an index refers to a statistical measure that tracks the performance of a group of assets or a basket of securities, such as the S&P 500, which represents the stock performance of 500 large companies listed on stock exchanges in the United States. In computing, an index is a data structure used to improve the speed of data retrieval operations on a database by minimizing the number of disk accesses required when a query is processed. It functions similarly to an index in a book, but instead of guiding a reader to a page, it guides the database software to the location of the desired data. In each of these contexts, the underlying principle of an index is to provide an organized method for tracking and accessing information efficiently.