From Seo Wiki - Search Engine Optimization and Programming Languages
Link flooding, link injection, or link spamming is the act of inserting links to promote a service, wiki, internet forum, blog or company. Often this technique is used to increase search engine rankings. Link flooding/injection also occurs frequently in blogs with spam comments. Link flooding is also considered to be a type of spamming.
Method of insertion
Methods of link insertion can include cross-site scripting and comment spam.
Wikipedia bans users who inject links or promote products. Wikipedia also has the no more links template to place on "External Links" sections of articles. There are also other ways to prevent link flooding.