Masters is the name of a degree that you often obtain after the Bachelors. The degree gives you the certificate of higher study in a certain area, making you the so-called master of tat field. The duration varies for different fields. For instance, it is 2 years for minor sciences, while it is 4 years or longer for medicine.
It is important to get it as it increases your worth and helps you follow your career to the very end. Moreover, you can excel based on your qualification as well and demand a better package as you have more knowledge of the subject than a simple bachelor degree would.
There are many different things that are referred to as "masters" but I think here you may be referring to a masters degree. A masters degree is typically a 2-year program that follows a bachelors degree. A masters degree is focused on a specialty and provides specific training related to a particular career path.
For some career paths it is important to have a masters degree, especially if you are going into research, academia, or a highly specialized field.