Which of the following best describes a search engine?

A search engine is primarily a website that enables users to locate other websites by entering specific keywords or phrases. It functions by indexing vast amounts of information from the web and organizing that data to facilitate quick and efficient retrieval in response to user queries. When a user types in a keyword, the search engine processes this information to present a list of relevant websites organized by relevance and authority.

In contrast, other options do not accurately describe what a search engine is. Antivirus software focuses on protecting computers from malicious threats rather than locating information online. A platform for hosting web applications refers to a service used to run and manage software applications on the internet, which does not directly correlate with the function of searching for information. Lastly, a network protocol for emails pertains to the rules and standards used for email communication, which is also distinct from the searching capabilities of a search engine. Therefore, the characterization of a search engine as a website that helps find other websites based on keywords is precise and encompasses its primary function.