search engine

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A software program that searches a database and gathers and reports information that contains or is related to specified terms.
• noun A website whose primary function is providing a search engine for gathering and reporting information available on the Internet or a portion of the Internet.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun computing an application that searches for, and retrieves, data based on some criteria, especially one that searches the Internet for documents containing specified words

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun a computer program that retrieves documents or files or data from a database or from a computer network (especially from the internet)