Meta tags are defined in section of an HTML page and give extra information about the page. Google a few of the possible meta tags have a meaning, as in "meta tags can be browse."

Meta Description

The Description Meta Tag is intended as a brief summary of the contents of a page and should be unique for each page of a domain. This day has, according to the Google Webmaster Central blog post Google does not use the keywords meta tag in web ranking does not affect the ranking of a website:

[...] Even though we sometimes BACKGROUND OF THE description meta tag for the snippets we show, we still do not the ranking of BACKGROUND OF THE meta tag description. [...]

However, it is possibly for the generation of snippets used. However, there is no guarantee, because Google adjusts the snippet of the query.

Meta Keywords

The keywords meta tag does not affect the ranking of a website in the SERPs and has otherwise no significance for Google. It is mentioned here only because it is a common myth that this day can affect the ranking of a page. There are several screencasts from Matt Cutts that refute that.

Robots

The robots meta tag controls the behavior of search engines on the page on which it is placed. It can take the following values:

noindex -> Prevents indexing a page
nofollow -> Prevents hyperlinks for more Crawlingvorgänge be used
nosnippet -> Prevents the display of snippets
noodp -> Prevents the description text of the ODPOpen Directory (if present) is used as a snippet
noarchive -> Prevents Google keeps a cached version of this page
unavailable_after: [date] -> Prevents from crawling specified by [date] date
noimageindex -> Prevents the pictures on this page show up in Google Image Search

None of these values ??has influence on the ranking. If the date is not set, it is assumed by default to the value "index, follow". This indicates that the page should be indexed and that the linked sites may be crawled.

Refresh

The refresh meta tag causes a redirect to Google as a 301 redirect is handled. The day has however been deprecated by the W3C and should no longer be used.

Dublin Core standard

The Dublin Core standard is another method available to provide an HTML document with meta information. It has some advantages over conventional meta tags through the standardization of certain values. Regarding the search engine optimization but it does not bring any advantages to meta-data according to the Dublin Core standard uses. This was, for example, 2005 by www.webology.ir investigated.