Meta Tag Overview -- For SEO

What are meta tags? They are information inserted into the "head" area of your web pages. Other than the title tag , information in the head area of your web pages is not seen by those viewing your pages in browsers. Instead, meta information in this area is used to communicate information that a human visitor may not be concerned with. Meta tags, for example, can tell a browser what "character set" to use or whether a web page has self-rated itself in terms of adult content
It is very important to use META Tags as well as a good TITLE if you expect to be found in most search engines. Note that META Tags are not the only thing search engines will look at when ranking your sites; and, also some search engines will ignore META Tags completely.

 

Title

The HTML title tag isn't really a meta tag, but it's worth discussing in relation to them. Whatever text you place in the title tag (between the TITLE and /TITLE portions as shown in the example) will appear in the reverse bar of someone's browser when they view the web page. 
It should be a concise, one-line summary of what the page is about. Bear in mind that users may not reach your document through your homepage, but directly using a search engine or link at another site, so the title should ideally be self-sufficient. If this is a company website, try to include the name of your company here also.

Keywords

Comma-separated list of key words for indexing your document.

The meta keywords tag allows you to provide additional text for crawler-based search engines to index along with your body copy.
The "keywords" should be related to the contents of that particular page, not the entire site. Think about using misspelled words too. Keywords may be separated by a space or a comma or a comma followed by a space.

Description

A "must have" for all web pages. Used by many search engines for indexing. The "description" <meta> tag is also commonly displayed by search engines as the summary of the web page. The "description" should be related to the contents of that particular page, not the entire site.
Many robots use the first few lines of text as a description if the Description tag is not present. For documents using frames, it is possible that there is no such text present. Try to include your company name or website name here also. Use keywords in your description.

Author

The author META tag defines the name of the author of the document being read. This tag is not widely supported but is recognized as part of the META Tag standard. Supported data formats include the name, email address of the webmaster, company name or Internet address (URL). The most common format is to insert the name of the person or organization and a contact email address. 

META Tag Usage

META Name:	"Author"
General Usage:	<META name="Author" content="Author Information">

Search Engines Usage

Although not many search engines look specifically for the Author META tag, it clearly defines who is the author and/or the responsible party for making updates to the webpage(s).

 

Robots

The Robots META tag (when supported) allows you to control which pages you would like spidered by the search engine robot. You can define which pages to follow, which to index and which to ignore completely.

<META NAME="ROBOTS" CONTENT="ALL | NONE | NOINDEX | NOFOLLOW"> default = empty = "ALL" "NONE" = "NOINDEX, NOFOLLOW"

The filler is a comma separated list of terms:
ALL, NONE, INDEX, NOINDEX, FOLLOW, NOFOLLOW.

 This tag is meant to provide users who cannot control the robots.txt file at their sites. It provides a last chance to keep their content out of search services. It was decided not to add syntax to allow robot specific permissions within the meta-tag.

INDEX means that robots are welcome to include this page in search services.

FOLLOW means that robots are welcome to follow links from this page to find other pages.

So a value of "NOINDEX" allows the subsidiary links to be explored, even though the page is not indexed. A value of "NOFOLLOW" allows the page to be indexed, but no links from the page are explored (this may be useful if the page is a free entry point into pay-per-view content, for example. A value of "NONE" tells the robot to ignore the page.

Charset

Specifies the character encoding for the page. This tag is required on each XHTML page so it will validate properly.

<meta http-equiv="Content-Type"
content="text/html; charset=ISO-8859-1" />

A variety of character encoding values are available. The one shown is common and appropriate for most websites.

The Language META tag declares the natural language of the document being indexed. Search engines which index sites based on language often read this tag to determine which language is supported.

The Ratings META tag tells the search engines whether the page is acceptable for all audiences, or adult audiences only.

Object Type

Category information of value to some for search engines or directory indexers. You have several choices, but the default is document.

Revisit 

The Revisit META tag defines how often a search engine or spider should come to your website for re-indexing. Often this tag is used for websites that change their content often and on a regular basis. This tag can also be beneficial in boosting your rankings if search engines display results based on the most recent submissions.
 

META Tag Usage

META Name:	"Revisit-After"
General Usage:	<META name="Revisit-After" content="X Days"> Note: X indicates a number

Search Engines Usage

The Revisit META Tag is used by search engines as a means to indicate how often a web page should be revisited for re-indexing. This tag is supported by many search engines and should be made use of if your content changes on a regular basis.

Expires

The Expires META tag defines the expiration date and time of the document being indexed. If your website is running a limited time event or there is a preset date when your document will no longer be valid, you should include the Expires tag to indicate to search engines when to delete your webpage from their database.

The expires tag is commonly used in conjunction with the Revisit Tag as a means to get search engines to re-visit a website every few days. This is commonly used by websites who update their content frequently and want search engines to have a fresh copy of their content.

META Tag Usage

META Name:	"Expires"
General Usage:	<META name="Expires" content="Tue, 01 Jun 2001 19:58:02 GMT"> Note: Requires RFC1123 date as shown above

Search Engines Usage

The Expires Meta Tag is principally used as a means to indicate to search engines a fixed date when they should remove your page from their database. If your page will expire at a preset date, it is advisable to set this tag a day or two before you plan the expiry such that search engines have time to remove you and avoid users getting an expired document or an error.