What is goal in Google Analytic ?

Hi Everyone !! What is goal in Google Analytic and how to set Goal please describe it.

Goals As the name suggest is the outcome that you predict From your efforts.
Every site that is into existence have some goal Like some want to sell something, some site want user to stay on their page and read whole article, some site have querry forums that they want user to fill and they follow that querry offline.
These are goals that you set in google analytic(Or any analytic softaware) so that you can measure how much fruitful your efforts is ?
Suppose you want to sell T-shirts on your site, You set that goal in google analytic(put google provided code on your "thank you" page,So that google can came to know that's the required action you want your to follow ) . A user come on your site and purchase the T-shirt, that's mean you get 1 goal completed on your site.

You have to tell Google Analytics to keep track of what's critical to your business – and you do this with goals.

Goals in Google Analytics allow you to track specific user interactions on your site. These user interactions can be anything including form submissions, button clicks, ebook downloads, and more. When a website visitor performs the specific action that you've defined as a goal, Analytics records that as a conversion.

What is goal in Google Analytic ?