Meta tags are the HTML tags which provide information about the content of a webpage. They tell what the page is about, who has created the page, when it is updated, keywords used to represent the page,etc. This information helps search engines index the webpage so that users looking for that or similar information could find it.
Meta tags are placed inside the head of HTML, i.e. <head>meta tags</head>. Users browsing your site cannot see them but the search engine can see them to get a brief idea about your keywords and to know what your site is about.
There are three types of meta tags
Title tag: It is the title text which appears in search engine listings on the title bar of the browser window.
Meta description tag: It is the brief summary of the content of your page. It appears below the URL of your page in search engine listings.
Meta keywords tag: It is the place where you put all of your important keywords and phrases that describe the content of your page.