What are Meta Tags?
Meta tags are snippets of text that describe a page’s content; the meta tags don't appear on the page itself, but only in the page's source code. Meta tags are essentially little content descriptors that help tell search engines what a web page is about.
The only difference between tags you can see and tags you can't see is location: meta tags only exist in HTML, usually at the "head" of the page, and so are only visible to search engines.
The "meta" stands for "metadata", which is the kind of data these tags provide - data about the data on your page.
There are two important type of meta that developers can use:
The title tag is the title text that is shown in search engine listings. I know that this is not necessarily a meta tag, but it similarly functions like one.
The meta description tag is where you would want to put your site’s summary. This is where you put what your site is all about and what you are offering people. It should not be too long because the search engines only read up to a certain number of words.
How much time should I spend on meta tags, and which ones matter?
Meta tags are a great way for webmasters to provide search engines with information about their sites.
Meta tags can be used to provide information to all sorts of clients, and each system processes only the meta tags they understand and ignores the rest. Meta tags are added to the <head> section of your HTML page.