An index may refer to any of the following:
1. An index is a method of sorting data by creating keywords or a listing of the data. A great example of an index of Computer Hope's hardware listing.
2. When referring to the Internet or web pages, an index is a file named as index.htm, index.html, index.asp, or index.php. The index file is the first file loaded when accessing a directory on a website. For example, when visiting Computer Hope at https://www.computerhope.com you are really accessing https://www.computerhope.com/index.htm since both addresses point to the same file. If the index file is missing from the directory and directory indexing is not disabled in the .htaccess file any visitor accessing that directory on the Internet will see a list of all the files in the directory instead of a web page or error message.
3. An index may also be a brief summary or section of a page or pages of documents created to allow another program or search engine to capture keywords or search several documents without having to open multiple files.
4. When referring to a search engine, database, or other search, indexing is a term used to describe the process of a computer or script gathering information about files to make the search process faster.