Metatag For Keyword

The HTML meta Element Metadata is information about data.
The <meta> tag provides metadata about the HTML document. Metadata will not be displayed on the page, but will be machine parsable.
Meta elements are typically used to specify page description, keywords, author of the document, last modified, and other metadata.
The <meta> tag always goes inside the head element.
The metadata can be used by browsers (how to display content or reload page), search engines (keywords), or other web services.

Keywords for Search Engines
Some search engines will use the name and content attributes of the meta element to index your pages.
The following meta element defines a description of a page:

<meta name="description" content="Free Web tutorials on HTML, CSS, XML" />

The following meta element defines keywords for a page:

<meta name="keywords" content="HTML, CSS, XML" />

The intention of the name and content attributes is to describe the content of a page.
Note: A lot of webmasters have used <meta> tags for spamming, like repeating keywords (or using wrong keywords) for higher ranking. Therefore, most search engines have stopped using <meta> tags to index/rank pages.