目录是由人为编辑的搜索结果。大多数目录依靠的是人为提交而不是爬行器（spider）。
Directories are search results that are edited by people. Most directories rely on human commits rather than spiders.
竞价（bid）为每个搜索引擎引荐向搜索引擎支付发费用，用以保证在付费搜索结果的排名。其最简单的形式，付费搜索结果显示出价最高一方的网页链接在结果列表的顶端，并且竞标方每次在访客点击竞标方的链接时付钱给搜索引擎。
Bidding (bid) refers to each search engine to pay a fee to the search engine to ensure the ranking of paid search results. In its simplest form, paid search results show that the page link of the highest bidder is at the top of the result list, and the bidder pays the search engine every time the visitor clicks the link of the bidder.
关键字、关键词和关键描述标签短语（Keyword、keyterm 和 keyphrase）
Keywords, keywords, and key description tag phrases (keyword, KEYTERM, and keyphrase)
关键字、关键词和关键描述标签短语是 Web 站点在搜索引擎结果页面（也称为 SERP）上排序所依据的词。根据站点受众的不同，您可以选择一个单词、多个单词的组合或整个短语。为简化起见，本文将使用关键词 这个术语表示所有这三种类型。
Keywords, keywords, and key description tag phrases are the words by which a web site sorts on search engine results pages (also known as SERPs). Depending on the audience of the site, you can choose one word, a combination of multiple words, or an entire phrase. For simplicity, this article uses the term keyword to refer to all three types.
关键词密度（keyword density）也被称为搜索项密度（term density ），是关于特定搜索请求的项在网页上所有项中的比率。例如，如果你想要的200 个词的网页就是关键词“失眠症”被找到，而你的网页上这个词出现了12 次，你网页上这个词的关键词密度是6% （12/200）。搜索引擎通常认为有 6~7%关键词密度的网页是很高质量的网页。
Keyword density, also known as term density, is the ratio of items in a specific search request to all items on a web page. For example, if the 200 word web page you want is the keyword "insomnia" found, and the word appears 12 times on your web page, the keyword density of the word on your web page is 6% (12 / 200). Search engines usually think that pages with 6-7% keyword density are high-quality pages.