black hat (seo) (chapeau noir) : illegal or dishonest ways to get one’s website highly ranked in search engines. The activity of improving rankings is called search engine optimization (SEO)
When an internet company uses black hat SEO techniques, they are trying to trick the search engines by over-exploiting the search criteria.
A good, honest technique is called ‘white hat’. Search engines find websites by looking for keywords related to the content in the text of the website. Someone who speaks French and wants to learn English for free would type words like ‘apprendre l’anglais gratuitement’ or ‘cours d’anglais gratuit’. This words appear quite frequently on my site, so it’s likely that the search engines will list my site in its results.
A dishonest ‘black hat’ technique would consist of putting images (sometimes so small they can’t be seen) with alt tags loaded with keywords: anglais,apprendre,anglais gratuit, anglaisfacile). Or they my have a white page with white text, invisible to people but visible to search engines, again full of keywords.
Most search engines have taken into account dishonest optimization techniques and their algorithms have been set to ignore them.