rel=”nofollow”, is said to be the next biggest thing to be used by shady webmasters engaging in reciprocal link exchanges. This attribute was introduced by Google as a means to prevent the problem of comment spamming in weblogs, also called “Blogs”, and it looks to be adopted by all other major search engines such as Yahoo! and MSN.
“rel” is an attribute, not a tag
rel=”nofollow” has been inaccurately called a HTML tag. It is in fact an attribute that can be added to HTML tags, similar to adding the attribute “width” to HTML tags such as img or table