Wolfram Alpha (also written WolframAlpha and Wolfram|Alpha) is an ‘answer-engine’ (not a search engine) developed by Wolfram Research.
It is an online service that answers factual queries directly by computing the answer from structured data, rather than providing a list of documents or web pages that might contain the answer as a regular search engine such as Google might.
It was announced in March 2009 by British scientist Stephen Wolfram, and was released to the public on May 15, 2009.
Its usefulness for Siri users becomes clear when asking specific questions such as - How many days until Christmas?.
Rather than return a list of search results in Google, Siri uses Wolfram Alpha to generate what it believes is the correct answer.
It’s not always entirely accurate but as the service is developed it will offer an incredibly quick and powerful way to get information.