Meta means about. It's abstracted from the subject.
In terms of SEO there are three most common used meta tags: Meta title, description and keywords.
Title: The meta title is a title you give your webpage within the meta tags so that when a person sees a link to your page from the search engine it has a title to go with it.
In the HTML coding of a webpage, the meta title is located in the head of the document. It is set apart by TITLE tags, <title>This Is the Meta Title</title>.
Meta keywords were used to be sure that each keyword accurately reflects the content of your pages. But, meta keywords are not in use nowadays, search engine not using meta keywords to know the content anymore.
Meta description is used to describe the content of your web page. It is a short paragraph placed in the HTML header tag of the webpage. The ideal length of meta description is in between 140 to 160 characters (with space).