Updated: 10/04/2017 by Computer Hope

An index may refer to any of the following:

1. An index is sorting data by creating keywords or a list with pointers to where further information about the keyword is found. For example, in many books, an index is found at the back with keywords and where they're found in the book.

Computer Hope uses its computer dictionary as an index for its website. For example, you could visit our Computer Dictionary - A page to see an index of all computer-related terms starting with the letter 'A.' Also, many of our terms (including this one) have an "Also see" section at the bottom with related links.


See our site map for an overall index of the Computer Hope site.

2. With the Internet and web pages, an index is a file named 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, you're accessing since both addresses point to the same file.

Suppose the index file was missing from the directory and directory indexing is not disabled in the .htaccess file. In this case, the visitor would see all directories and files in that directory instead of a web page or error message.

Why are there different types of index files?

The file extension used for the index file is dependent on the technology used for the website. For example, index.htm and index.html are both HTML only files. However, index.php is for a dynamic website that uses PHP (PHP: Hypertext Preprocessor) scripting language to create the page.

What if there are multiple index files?

If the directory contains multiple index files (e.g., index.html and index.php), the web server loads the highest priority index first. For example, if the server has the loading order index.htm, index.html, index.php, and then index.asp, it would use and load index.html. If you wanted the PHP file to be used instead, the index.html file would need to be deleted, or the server load order would need to be changed.

3. An index may also be a summary or section of documents created to allow another program or search engine to capture keywords or search several documents without opening multiple files.


This index is often called a site map.

4. With a search engine, database, or another search, indexing describes a computer or script that gathers information about files to make the search process faster. Once the information is gathered, it's placed into a single file or database, allowing the search to use that single source instead of looking through multiple files.

5. With computer programming, an index is elements of an array.

Database terms, Index finger, Internet terms, Search engine, Site Map