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Keyword density is the percentage of times a keyword or phrase appears on a web page compared to the total number of words on the page. It is advised to keep the keyword density lower than 3%. Anything more than that and there could be a risk of SPAM penalties.
A practical approach is to examine the top ranking web pages for a particular keyword and aim for similar densities.
An alt tag, also known as "alt attribute" and "alt description," is an HTML attribute applied to image tags to provide a text alternative for search engines.
According to google:
By adding more context around images, results can become much more useful, which can lead to higher quality traffic to your site.
Having a large image with an ALT tag that includes the keyword could make search engine give more relevance to the page.
Link backs are the opposite of backlinks. A link back is where your page links to other high authority pages. The idea behind this technique is that your webpage going to get better ranking when it appears as the reference page for target keyword.
The keyword position is the position of the keyword in relation to the whole content:
Internal Links are links that point to another webpage on the same website. Internal links have many purposes, including but not limited to:
Power words are words that are used to trigger a response or action. Tested for “phraseology,” these select words have been proven to elicit an emotional response from readers.
Click-through rate is a defining SEO factor. If your search results get more clicks than what is expected for its search results position, the search engine assumes your link to be more relevant and of more interest and provides it with a boost.
According to Google's own records, the search engine uses more than 200 ranking factors. ↩
A permanent static hyperlink to a particular web page or entry in a blog. ↩
"Keyword stuffing" refers to the practice of loading a webpage with keywords or numbers in an attempt to manipulate a site's ranking in Google search results. ↩