After understanding what SEO is, we also need to explore a series of SEO terms to help us to more effectively design SEO strategies in the future. 1. A web crawler, which systematically browses the Web to collect data from webpages. Typically search engines (e.g. Google, Bing, etc.) use crawlers to build indexes. 2. Index, include webpage data crawled by web crawlers into the search engine database to create a website index. The search engine will search for relevant results on the index page when the searcher enters keywords. 3. On-site Optimization, optimize the background structure of the website. For example, put keywords in URL, article title and Headings such as H1, H2 and H3. You can also start with HTML grammar, and replace the image to be downloaded with Alt Text, which helps web crawlers access and enhance Correlation. 4. Off-Site Optimization, relying on other sites and other factors to optimize, so as to improve the score of the site in the site index, so that the site has a greater chance of appearing in high-ranking search results. 5. White Hat SEO, use the correct method to improve the search results of search engines, such as improving the content of the website, so that readers can get substantial help from the content of the website. 6. Black Hat SEO, in order to gain free traffic, use deceptive methods to increase the ranking of the website in the search results. For example, enter a large number of keywords in the website and change the font to the same color as the background. Relevance to become a high ranking search result. 7. Grey Hat SEO, between the white hat and the black hat. Although it is not as deceiving as the black hat, it is also more tricky than the white hat. For example, it will rewrite some articles to pretend to be original to improve ranking.