What is Google Bomb?

Legal Definition
The terms Google bomb and Googlewashing refer to the practice of causing a web site to rank highly in web search engine results for unrelated or off-topic search terms by linking heavily. In contrast, search engine optimization (SEO) is the practice of improving the search engine listings of web pages for relevant search terms.

It is done for either business, political, or comedic purposes (or some combination thereof). Google's search-rank algorithm ranks pages higher for a particular search phrase if enough other pages linked to it use similar anchor text. By January 2007, however, Google tweaked its search algorithm to counter popular Google bombs such as "miserable failure" leading to George W. Bush and Michael Moore; now, search results list pages about the Google bomb itself. As of January 2016, the first result in a Google search for "miserable failure" is the Wikipedia article defining Google bomb. Used both as a verb and a noun, "Google bombing" was introduced to the New Oxford American Dictionary in May 2005.

Google bombing is related to spamdexing, the practice of deliberately modifying HTML to increase the chance of their website being placed close to the beginning of search engine results, or to influence the category to which the page is assigned in a misleading or dishonest manner.

The term Googlewashing was coined by Andrew Orlowski in 2003 to describe the use of media manipulation to change the perception of a term, or push out competition from search engine results pages (SERPs).
-- Wikipedia