Meta tags are HTML codes that are inserted into the header on a web page, after the title tag. In the context of search engine optimization, when people refer to meta tags, they are usually referring to the meta description tag and the meta keywords tag.
The meta description tag and the meta keywords tag are not seen by users. Instead, these tags main purpose is providing meta document data to user agents, such as search engines. In addition to the well-known meta description and meta keywords tags, there are other useful meta tags, including the meta http-equiv tag, meta refresh tag, the meta robots tag, the meta copyright tag, and the meta author tag, etc. These tags are used to give web browsers and search engine spiders directions or data on various information.

see how it looks like in HTML