Hop bursting is a technique where all hops are added late, with 30 minutes or less left in the boil.
Hops contain lots of oils that impart aroma and taste into the final beer. However, when added early in the boil, most of these volatile oils boil off. Thus the oils from bittering hops added early in the boil tend to boil off and the hops only contribute to the bitterness of the beer.
By adding more hops later in the boil, you can still achieve the same bitterness but also keep around more oils and get more hop aroma and flavor in the beer. Brewers do this by adding a "burst" of hops around the 30 or 40 minute mark of the boil, and continuing to add lots of hops until the end of the boil.
Since the bittering hops are added later in the boil, they add more aroma and flavor, but less alpha acids, so more are needed to achieve the same bitterness. John Palmer has a great section about how to calculate IBUs based on hop additions, it's basically:
Weight (oz.) * % alpha acids * 75 * Utilization(time, gravity) / Volume of Wort (gallons)
Where utilization is a number based on the length of time the hops are boiled for and the gravity of the wort (he has a chart for looking up this number on the site).
Alternatively, you could use a tool to make these calculations for you. I prefer Beer Calculus. Here's an example of a recipe that uses a burst of hops late in the boil for lots of hop aroma and taste.