Definition of "ballooning"

This major artery from the heart to the lower body, the aorta, can indeed develop aneurysms. These balloonings of the shape of the normally straight artery may cause no bother, no symptoms and no complications.

2013, Margaret McCartney, The Patient Paradox, page 95

Like most human activities, ballooning has sponsored heroes and hucksters and a good deal in between. For every dedicated scientist patiently recording atmospheric pressure and wind speed while shivering at high altitudes, there is a carnival barker with a bevy of pretty girls willing to dangle from a basket or parachute down to earth.

2013 June 7, David Simpson, “Fantasy of navigation”, in The Guardian Weekly, volume 188, number 26, page 36