Slow down your rocket in an upper atmosphere. Ballute = parachute + baloon = an alternative to a heatshield.
Sample usage: Duna aerocapture and aerobraking, Kerbin reentry for reusable stages etc.
stock aero = none.
FAR: Module Manager by Sarbian and RealChute by stupid_chris
RealChute by stupid_chris - especially when with FAR aerodynamics. Config for RealChute is already included in the mod.