Description meta tags are important because Google might use them as snippets for your pages. Note that we say "might" because Google may choose to use a relevant section of your page's visible text if it does a good job of matching up with a user's query. Adding description meta tags to each of your pages is always a good practice in case Google cannot find a good selection of text to use in the snippet. The Webmaster Central Blog has informative posts on improving snippets with better description meta tags18 and better snippets for your users19. We also have a handy Help Center article on how to create good titles and snippets20.

Google used to make much of its ad hoc keyword search functionality available as well, but now the Keyword Planner is behind a paywall in AdWords as a premium feature. Difficulty scores are inspired by the way Google calculates its Competition Score metric in AdWords, though most vendors calculate difficulty using PA and DA numbers correlated with search engine positions, without AdWords data blended in at all. Search Volume is a different matter, and is almost always directly lifted from AdWords. Not to mention keyword suggestions and related keywords data, which in many tools come from Google's Suggest and Autocomplete application programming interfaces (APIs).

You should build a website to benefit your users, and any optimization should be geared toward making the user experience better. One of those users is a search engine, which helps other users discover your content. Search Engine Optimization is about helping search engines understand and present content. Your site may be smaller or larger than our example site and offer vastly different content, but the optimization topics we discuss below should apply to sites of all sizes and types. We hope our guide gives you some fresh ideas on how to improve your website, and we'd love to hear your questions, feedback, and success stories in the Google Webmaster Help Forum1.
These cloud-based, self-service tools have plenty of other unique optimization features, too. Some, such as AWR Cloud and Searchmetrics, also do search position monitoring—which means tracking how your page is doing against popular search queries. Others, such as SpyFu and LinkResearchTools, have more interactive data visualizations, granular and customizable reports, and return on investment (ROI) metrics geared toward online marketing and sales goals. The more powerful platforms can sport deeper analytics on paid advertising and pay-per-click (PPC) SEO as well. Though, at their core, the tools are all rooted in their ability to perform on-demand keyword queries.
You can confer some of your site's reputation to another site when your site links to it. Sometimes users can take advantage of this by adding links to their own site in your comment sections or message boards. Or sometimes you might mention a site in a negative way and don't want to confer any of your reputation upon it. For example, imagine that you're writing a blog post on the topic of comment spamming and you want to call out a site that recently comment spammed your blog. You want to warn others of the site, so you include the link to it in your content; however, you certainly don't want to give the site some of your reputation from your link. This would be a good time to use nofollow.
This helpful tool scans your backlink profile and turns up a list of contact information for the links and domains you'll need to reach out to for removal. Alternatively, the tool also allows you to export the list if you wish to disavow them using Google's tool. (Essentially, this tool tells Google not to take these links into account when crawling your site.)
That's why PA and DA metrics often vary from tool to tool. Each ad hoc keyword tool we tested came up with slightly different numbers based on what they're pulling from Google and other sources, and how they're doing the calculating. The shortcoming of PA and DA is that, even though they give you a sense of how authoritative a page might be in the eyes of Google, they don't tell you how easy or difficult it will be to position it for a particular keyword. This difficulty is why a third, newer metric is beginning to emerge among the self-service SEO players: difficulty scores.
Difficulty scores are the SEO market's answer to the patchwork state of all the data out there. All five tools we tested stood out because they do offer some version of a difficulty metric, or one holistic 1-100 score of how difficult it would be for your page to rank organically (without paying Google) on a particular keyword. Difficulty scores are inherently subjective, and each tool calculates it uniquely. In general, it incorporates PA, DA, and other factors, including search volume on the keyword, how heavily paid search ads are influencing the results, and how the strong the competition is in each spot on the current search results page.

Website owners recognized the value of a high ranking and visibility in search engine results,[6] creating an opportunity for both white hat and black hat SEO practitioners. According to industry analyst Danny Sullivan, the phrase "search engine optimization" probably came into use in 1997. Sullivan credits Bruce Clay as one of the first people to popularize the term.[7] On May 2, 2007,[8] Jason Gambert attempted to trademark the term SEO by convincing the Trademark Office in Arizona[9] that SEO is a "process" involving manipulation of keywords and not a "marketing service."