A web search engine is a software system that is designed to search for information on the World Wide Web.

The search results are generally presented in a line of results often referred to as search engine results pages (SERPs).

The information may be a mix of web pages, images, and other types of files.

Some search engines also mine data available in databases or open directories.

Unlike web directories, which are maintained only by human editors, search engines also maintain real-time information by running an algorithm on a web crawler.

Google is an American multinational technology company specializing in Internet-related services and products.

These include online advertising technologies, search, cloud computing, software, and hardware.

An index term, subject term, subject heading, or descriptor, in information retrieval, is a term that captures the essence of the topic of a document.

Index terms make up a controlled vocabulary for use in bibliographic records.

They are an integral part of bibliographic control, which is the function by which libraries collect, organize and disseminate documents.

They are used as keywords to retrieve documents in an information system, for instance, a catalog or a search engine.

A popular form of keywords on the web are tags which are directly visible and can be assigned by non-experts.

Index terms can consist of a word, phrase, or alphanumerical term.

They are created by analyzing the document either manually with subject indexing or automatically with automatic indexing or more sophisticated methods of keyword extraction.

Index terms can either come from a controlled vocabulary or be freely assigned.

Free software, freedom-respecting software, or software libre is computer software distributed under terms that allow the software users to run the software for any purpose as well as to study, change, and distribute the software and any adapted versions.

Free software is a matter of liberty, not price: users, individually or collectively, are free to do what they want with it, including the freedom to redistribute the software free of charge, or to sell it, or charge for related services such as support or warranty for profit.

The Internet is the global system of interconnected computer networks that use the Internet protocol suite (TCP/IP) to link devices worldwide.

It is a network of networks that consists of private, public, academic, business, and government networks of local to global scope, linked by a broad array of electronic, wireless, and optical networking technologies.

The Internet carries an extensive range of information resources and services, such as the inter-linked hypertext documents and applications of the World Wide Web (WWW), electronic mail, telephony, and peer-to-peer networks for file sharing.