It's simply a computer program that allows the Internet users to search for information stored on different computers all around the world. Directory It allows you to search the Internet using a subject. It's also called a subject search. Some search tools understand natural language. Notice the differences of the result given to you.
Some tools are smarter than the others.
This program searches a number of search engines simultaneously. This one seraches consecutively, rather than simultaneously. Here are some special exercises for searching. Don't forget the question mark at the end. Use Boolean operators.