For search engine crawlers meta tags provide comprehensive information at a glance. For someone who is visiting your website ,this information is not provided and the most popular among them is the description tag. It can be incorporated in any area of your page. A couple of years back, they were the most important tool from the point of view of Search engine optimization. Between the rankings in the search results and the keywords in the meta tags, there was a direct correlation. A well known fact is that algorithms have got better and the stature of meta tag is evolving day by day.
A meta title tag is an HTML element that specifies the title of a web page. Title tags are displayed on SERPS (search engine results pages) as the clickable headline for a given result, and are important for usability, social sharing and SEO.
In short it is a short description of your website, and in the process, points the website to search engines to themes or topics which is relevant to your website. Some search engines like Google go on to use them as a summary of the listings in the search page results. If meta descriptions are properly scripted it will draw traffic to your website.
The concept is the same as working on the list of keywords which is relevant of your page. Most of the search engines will not take this point into consideration, but you can work on your own set of meta keywords. To boost the ratings of your search engines you can look for alternate spellings or words that are commonly misspelled.
Here you clearly outline the pages that you do not want to be indexed or crawled. There are chances that you want to keep some of the contents, but do not want it indexed . You can list these pages in the Meta robots tag and this is one way to exclude them. Another alternative is using the robots. Txt line and this is a better method.