Meta Tag:
HTML meta tags are referred as tags of page data head tags of a document's HTML code. Actually these are hidden keyword who set in the code. These are invisible to visitors but are visible and readable by Search Engines.
Example:
The meta tag is used to represent metadata regarding HTML document. Meta tags in general are used to specify author of document, keywords, page description and similar metadatas. They are commonly used by search engines, browsers and web services.
Meta tags are HTML tags that are read by search engines. They tell they search engines the description of your site, the keywords attached to your site, and anything else important that you think the search engine should know about it.
Meta Tags look like this
Note: Google does not read Meta keywords, and takes limited weight for meta description. Bing reads both
Meta in any language and HTML is no exception is the raw data that defines a page. What you are saying to the computer or reader is "I am a Letter", "This letter is about me moving house", and in HTMLs case these are some key words "united,kingdom,midlands,London,moving,house".
They are set in the header or rather <head> </head> tags.
Examples:
<meta http-equiv="Content-type" content="text/html; charset=utf-8" /> - Tells the browser that this is written in HTML using that character set.
<meta name="description" content=" This letter is about me moving house"/> - Description Meta
<meta name="keyword" content="united,kingdom,midlands,London,moving,house"/> - Keyword Meta
There are more Meta tags than this of course.
The reason why we use them is because of Spiders from Google can pick up on the Meta tags. So your title or rather <title>I am a Letter</title> becomes the title in the search engine and then the description is from the meta along with the keywords.
Meta tag gives all the detail about metadata of the HTML document. <meta charset="UTF-8"> is an example of Meta tag.