The META tags are used to provide extra information about a web page.
There was once a time where a good search engine ranking could be
achieved by simply changing the value of the META tags. However these
days are long gone. Nowadays the META Tags are decreasing in
importance in the eyes of the search engines who are using more
sophisticated methods of ranking pages (namely link popularity,
optimized anchor text).

There are many different types of META tags but the one that can
affect ranking are the Keywords META tag and the Description META tag.

Keywords META tag:

This tag contains keywords relevant to a page. In the past search
engines referenced this to determine how to rank a particular page.
However many people started to abuse this and stuffed the tag with
keywords that were not relevant to the content of the page. This
confused search engines and subsequently returned weaker search
results. To combat this less and less emphasis has been placed on the
Keywords META tag. However this does not mean that it is entirely
useless. Here are some reasons to still include it:

* Some search engines still use it

Although most search engines do not use the tag there are undoubtedly
still some that do. For this reason place around 15-20 keywords
relevant to your site or page into the tag. Do not attempt to cheat
the search engines by repeating keywords as this is considered
spamming and they may look unfavourably on this.

* Account for misspellings of keyphrases

People can misspell certain keyphrases that you may be optimizing for
so it is common to place these misspellings into the Keywords META
tag. This allows you to rank in search engine results for misspellings
without having to represent them on the actual content of your page.

Description META tag:

In the past this tag was used to specify the text that would appear in
search engine results alongside the link to your site. Keywords could
be placed into this text to influence ranking. However it was abused
similar to the Keywords META tag and has befallen the same fate,
meaning it is not as useful as it once was. Some search engines do not
display it in their results (most notably Google, which retrieves the
text from content on your page) and do not use it to rank a site.
Having said that some search engines do still use it so again it is a
mistake to ignore it completely.

Descriptions placed into this tag should, strangely enough, be very
descriptive of the page or site they reside in. Include a few relevant
keywords/keyphrases that you are optimizing for in the description and
try to limit its length to 25-30 words. Also try to use no more than
two sentences.

Summary:

Although not as important as they once where, the META tags can still
influence a search engine when it comes to deciding whether your web
page is relevant or not.

Keywords META tag:

15-20 keywords, include misspellings of keywords/keyphrases

Description META tag:

Include keywords/keyphrases, 25-30 words, no more than two sentences.

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