What does it mean by 'releasing energy acquired during launch' for space shuttle?

they accelerated to orbital speed during launch. now they have to stop. just like a car accelerating, then stopping.

Basically it is kinetic energy, the energy of motion. Upon launch the shuttle was accelerated and maintained that speed to dock and undock with the space station. For the shuttle to slow down for landing it must rid itself of this excess energy. It does so by releasing (converting) this energy as heat as it encounters increasing air resistance in the thickening atmosphere along its return trajectory.

I t is potential energy do to the shuttle's height above the earth. It is really the energy obtained during falling in earth's gravity.