From the DOE website -
http://studentaid.ed.gov/PORTALSWebApp/stu...jsp?tab=funding
Subsidized Loans - A subsidized loan is awarded on the basis of financial need. If you're eligible for a subsidized loan, the government will pay (subsidize) the interest on your loan while you're in school, for the first six months after you leave school, and if you qualify to have your payments deferred.
Unsubsidized Loans - You might be able to borrow loan funds beyond your subsidized loan amount or even if you don't have demonstrated financial need. In that case, you'd receive an unsubsidized loan. Your school will subtract the total amount of your other financial aid from your cost of attendance to determine whether you’re eligible for an unsubsidized loan. Unlike a subsidized loan, you are responsible for the interest from the time the unsubsidized loan is disbursed until it is paid in full. You can choose to pay the interest or allow it to accrue (accumulate) and be capitalized (that is, added to the principal amount of your loan). Capitalizing the interest will increase the amount you have to repay.