Anchor text: the text of a link, the one which appear to human being.
Backlinks: it corresponds to the links which are pointing to a given web page.
Black hat techniques: techniques used to cheat within the search engine rankings.
Bots: also called crawlers, robots, spiders. Automatic program which look at web pages.
Cloaking: a black hat technique for search engines to see a content that you don't want to show to human being.
Crawl: corresponds to the fact that a bot is visiting a web page/resource.
Duplicate content: the fact that a content similar to the one you published is already available online (either through your website or not).
Grey hat techniques: search engines are not banning yet those techniques to rank websites higher but may do it in the near future.
Index: corresponds to the database of search engine. When your page is within this database it is indexed, when it has been kicked out it is de-index.
Keyword density: the number of time a given keyword appears on a web page.
Keyword stuffing: it means that you inserted too many times the same keyword. As a result your content is not digest and you get penalized because you tried to cheat on search engines.
Meta data: relates to data about a given page, not visible directly to the internet user but visible within the source code. Mainly used by robots.
Organic results: it refers to the SERP without paying.
PageRank: Google's innovation which make them popular as a search engine. It consisted in giving more values to some websites based on links they were receiving.
Rich snippets: extra data which can be inserted within the SERP, such as feedbacks, votes...
Robots.txt: a file to give directives to search engines robots.
Search: also named query, it corresponds to what people are searching for.
Search operators: special commands, search users can type in order to customize their search.
SEO: Search Engine Optimization. Methods used in order to make organic listings more visible within search engines.
SEA: Search Engine Advertising. Doing advertising thanks to search engines.
SERP: Search Engine Results Page, it correspond to the page listing the results of a search within a search engine.
Search operators: special commands used to filter SERP when doing a search.
Sitemap: an HTML or XML document listing all the individual URLs of a website.
Snippet: it corresponds to what search engines are listing within the SERP as an extract of your web pages.
Title tag: it corresponds to the title assigned to a web page.
White hat techniques: good practices recommended by search engines in order to rank a website within the search engine results pages.