The distinction between graduate school and professional school can often be blurred, with professional school being brought into the graduate school fold, but there is a difference between the two.
Graduate school programs are academic courses of study that offer more advanced programs of study (beyond a bachelor's degree) in certain disciplines. This can mean earning a master's degree on its own or as a step toward a PhD program.
Professional school programs help prepare students for careers in specific fields. Examples include medical, law, pharmacy, business, library, and social work schools. The length of these programs vary. Professional degrees are often required by law before an individual can begin a certain working in a particular occupation.
What's a terminal degree?
This is a term used mostly in the United States to denote the highest academic degree in a field of study. For many fields, this is the PhD, or doctor of philosophy degree. But other fields may have a master's degree as the terminal degree, such as master of fine arts (MFA) or master of landscape architecture.
You can find more information on these distinctions here.