Gran Fondo means long distance or great endurance in the Italian language.
Gran Fondos are usually 160-225 km long races or just rides. The majority of them offer an additional fondo course (120-160 km) and sometimes even a Medio Fondo course (under 120 km) for those not willing to ride the longer distance(s). These shorter courses are just abbreviated versions of the longer ones, mostly utilizing the same roads, but taking shortcuts to avoid some of the climbs.
Gran Fondo is meant for a wide range of cyclists with different goals and reasons for attending. Olympic champion Antonella Bellutti, writing for Il Gazzettino, expressed it well:
"What is it that attracts people from all over the world to massacre themselves on a such a difficult course, which calls for a 6:30 a.m. start, not to mention paying an entry fee that is not exactly small? I asked lots of participants and their answers were all the same: the satisfaction of completing such a hard test, pulled along by the enthusiasm and energy that so many people, all peacefully together, know how to produce! The satisfaction is that of being there, of being a protagonist in a moment of collective joy, of the sublimation of fatigue in the name of the bicycle...Young and old, men and women, competitive and touristic, well trained and less so, alone, couples, and groups, Italians and foreigners: a variegated universe but with one passion: the bicycle!"