AFAIK, burstable means that you commit to a certain amount of bandwidth, the minimum amount you pay for every month; and you are given a switch port which allows you to burst or use more bandwidth over your committed to amount as your needs dictate. This makes you open to 'overages' or charges for extra bandwidth, billed per megabit, over your initial minimum megabit commitment.
Dedicated means that your bandwidth (whichever way it is being billed) is ready and available for your use 24x7x365... and you have access to at least your minimum bandwidth commitment to burst up to, or use at any time you want without contending with other clients for the use of a limited amount of capacity.