Keywords are an essential aspect of SEO. However, they are not always as simple as they seem.
Short-tail keywords are a connection (usually a maximum of three) of keywords that produce a query within a search engine.
Although long-tail keywords generate less traffic overall, because of this and because they are so specific, they generate a higher conversion rate.
To create long-tail keyword phrases you will state your main keyword and then follow with a tail of further keywords/specifics.
Latent Semantic Indexing Keywords are terms or phrases that are conceptually-related or semantically related to your other keywords.
IN THEORY, rather than only searching for keyword usage on your site page, search engines work to understand the overall general topic of the page, which can be required through semantically-related keywords.
As contradictory as it may sound...
LSI keywords do not exist!
What I mean here is that these words do not exist for Latent Semantic Analysis, since search engines are unable to conduct such an analysis for the amount of sites contained on the internet.
Although LSI keywords do not exist for this purpose, semantically- and conceptually-related words do exist, and these keywords, which are often referred to as LSI keywords, do help to improve the search engine rankings of your pages.
What this means is that semantically-related keywords should still be contained within your content as they contribute to your sites ranking, but they do not, however, contribute to analysis for indexing.
It is key to bear in mind here that indexing and ranking are different processes. Indexing relates to a search engine's understanding of content, whereas ranking is the value and relevance of your page. Although these may seem similar, they are in fact different.
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