Excessive manipulation to influence search engine rankings, often for pages which contain little or no relevant content.
Search engine spamming often gets confused with legitimate search engine optimization (SEO). While there is much gray area between the two extremes, in their most clear cut forms the terms are very different. Spamming involves getting a site more exposure than it deserves for its keywords, leading to unsatisfactory search experiences. Optimization involves getting a site the exposure it deserves on the most targeted keywords, leading to satisfactory search experiences.
Irrelevancy – targeting keywords unrelated to the site/page.
Hidden Text – putting keywords where visitors will not see them, used to increase keyword count.
Hidden Links – putting links where visitors will not see them, used to increase link popularity.
Doorway Clutter – mass production of low-quality doorway pages, sometimes of the machine-generated variety.
see also: SEO Tools