An underserved area refers to one that has a significant discrepancy between the rest of the country as far as number of healt care providers.
An underrepresented area usually refers to schools, and it signifies an area that does not typically have entrants at the school in question. For instance, if students from Flint, Michigab do not usually attend U of M, then it is an underrepresented area.
There are scholrships available for people who want to serve underserved areas as physicians. However, most of them are actually loans, in that you commit yourself to working for this particular city/group for X amount of time if they contribute X dollars to your education. Similar to the military HPSP