Meta-elements, commonly called called meta tags, are pieces of information on an HTML page (web document), which are only interpreted by web-browsers and search-engines.
The attributes of a meta-element that are most relevant for the on-page optimisation of a website are:
The title element is not really a meta-element, but a dedicated HTML element interpreted by web-browsers and search-engines, and is often placed in front of other meta-elements within the HTML source code.
There are many other elements available and new elements being introduced as some become irrelevant. A list of elements can be found at the defining organisation, the World Wide Web Consortium (W3C).
Meta keywords – not important for SEO
The meta-element attribute “keywords” is no longer taken into consideration by Google and other search engines and is therefore not relevant for SEO.
Google doesn’t use the keywords meta tag in web search– Matt Cutts
What meta elements are important for Google?
A list of meta-elements (tags), attributes, including their content (content=”value”), that Google takes special care of can be found on the page Special Tags that Google understands.