Algorithm – The term search engines use for the formulae they use to determine the rankings of your Natural Listings. Search engines will periodically send a Spider through your Web site to view all its information. Their programs analyze then analyze this and other data to value your site and fix whether or not, and how high or low pages on your site will appears on various searches. These algorithms can be very complicated (Google alone currently uses 106 different variables) and search engines closely guard their algorithms as trade secrets.
For most web users it would be difficult to notice changes to search engine algorithms after they occur. The purpose of setting up and continuously updating these algorithms is to make searches more relevant for people wanting to find stuff and also to reduce bogus or junk results.
The best way to ensure getting noticed by search engines is still to create original content that is informative and engaging for readers. There really is no substitute for good writing.