SEO = search engine optimization
搜尋引擎最佳化(Search Engine Optimization，簡稱SEO)是一種利用搜尋引擎的搜索規則來提高目的網站在有關搜尋引擎內的提名的方式。由於不少研究發現，搜尋引擎的用戶往往只會留意搜索結果最開首的幾項條目，所以不少商業網站都希望透過各種形式來幹擾搜索引擊的排序。當中尤以各種依靠廣告維生的網站為甚。
所謂“針對搜尋引擎作最佳化的處理”， 是指為了要讓網站更容易被搜尋引擎接受。 搜尋引擎會將網站彼此間的內容做一些相關性的資料比對。 然後再由瀏覽器將這些內容以最快速且接近最完整的方式，呈現給搜尋者。
搜尋引擎優化對於任何一家網站來說，要想在網站推廣中取得成功，搜尋引擎優化都是至為關鍵的一項任務。同時，隨著搜尋引擎不斷變換它們的排名演算法規則，每次演算法上的改變都會讓一些排名很好的網站在一夜之間名落孫山，而失去排名的直接後果就是失去了網站固有的可觀訪問量。所以每次搜尋引擎演算法的改變都會在網站之中引起不小的騷動和焦慮。我們可以說，搜尋引擎優化也成了一個愈來愈複雜的任務。
Search engine optimization (SEO), a subset of search engine marketing, is the process of improving the volume and quality of traffic to a web site from search engines via "natural" ("organic" or "algorithmic") search results. SEO can also target specialized searches such as image search, local search, and industry-specific vertical search engines.
A typical Search Engine Results Page (SERP)As a marketing strategy, SEO considers how search algorithms work and what people search for in order to increase a site's relevancy. SEO efforts may involve a site's coding, presentation, and structure, as well as fixing problems that could prevent search engine indexing programs from fully spidering a site. Other, more noticeable efforts may include adding unique content to a site, and making sure that the content is easily indexed by search engines and also appeals to human visitors.
The term SEO can also refer to "search engine optimizers," a term adopted by an industry of consultants who carry out optimization projects on behalf of clients, and by employees who perform SEO services in-house. Search engine optimizers may offer SEO as a stand-alone service or as a part of a broader marketing campaign. Because effective SEO depends upon the source code of a site, SEO tactics may be incorporated into web site development and design. The term "search engine friendly" describes designs, menus, content management systems and shopping carts that are easy to optimize.
