A search engine is a computer-driven tool that helps people find information and specific websites online, and a directory is a list of websites that is compiled by a person with a specific goal in mind. The main difference between the two is that search engines produce results in response to a user input query, such as what one might enter into Google's search bar, while a directory is organized by a human and doesn't typically accept input from the user. One analogy that can be used to understand the difference between the two is comparing search engines to phone books, which contains all the contact information for a specific area, and directories to someone's personal address book, which only contains contact information that has been personally compiled.
Search engines effectively 'crawl' through all the available pages and information on the Internet to produce results based on a user's request, making them useful tools for those who are searching for specific information. Directories are typically organized around a single topic, such as the Foundation Directory Online's directory of grant makers and other beneficiaries of nonprofit organizations. While search engines are usually free for anyone to use, directories, including the Foundation Directory Online, may charge a fee for use.