Domain Authority (DA) represents the score for your entire website and is provided by Moz. Like Page Authority, this score can have a maximum value of 100, and factors in metrics such as the amount of links you have. DA is a measure of your overall domain strength.
Moz suggests that the best way to improve this score is to focus on your link profile. You will need to understand Google's Penguin algorithm and how it can affect your website. This most important thing about Penguin is to make sure your website's links are predominately brand keywords and NOT heavy on anchor text keywords.