Hidden text and links
The text a colored that is very near to the background color of the web page. It blends with the background color and be nearly invisible. Hidden links are links to other pages and sites that are seen by search engine spiders but not by surfers.This is done to increase the link count.

Cloaked pages
Normally associated with sites doing IP and USER-AGENT serving where the internet server will present a page that will vary based upon the visitor characteristics. This technology is commonly used to present differing content to each search engine or browser, thus a search engine seldom sees the same content that is presented to a browser. ANY cloaked site that filters based upon whether the visitor is a spider or a human, no matter how great the content, is considered spam by all of the major search engines.

Deceptive redirects
These are keyword-stuffed landing pages that quickly redirect to the real page.

Doorway pages
These are web pages that have been created for the sole purpose of ranking highly in the search results for one or two searchterms, and are not normally an integral part of the website.Doorway pages are created to do well for particular phrases.
They are also known as portal pages, jump pages, gateway pages, entry pages and by other names.

Duplicate sites or pages
Several tainted SEOs try to get increased visibility from search engines by making a mirror of the existing site or a few duplicates. Each site have a new, unique URL and unique domain name, a unique title and description tag, and body text slightly modified to focus on different keywords and phrases. They also try to give a newer, fresher look with different background colour and font.