There are three main flavors of Buddhism: Hinayana, Mahayana, and Theravada.
Hinayana (the 'lesser vehicle') is the oldest form of Buddhism and was founded by the Buddha himself. (Buddha is not a name. It means 'enlightened one'. The man's name was Gautama Shakyamuni. Similarly Christ means 'savior' in Greek. Jesus is a Grecization of Yeshua. His name in English would have been Joshua Josephson, but that doesn't have as religious a ring to it.) The basic idea was to find a way to get off the Hindu wheel of existence -- birth, death, reincarnation, followed by more birth and death, and so on. The plan was to improve one's karma by good deeds, by prayer, and clean living. Eventually one's karma gets so good that one achieves nirvana, which is bliss, peace, and nonexistence. Some in the West call Hinayana, the "don't be a schmuck" school of Buddhism. Actually I am the only one who calls it that.
Mahayana ('the greater vehicle') arose about three hundred years after Buddha lived. The basic motive for it was that rich people never made it to nirvana in Hinayana. Then as now, getting rich and not being a schmuck were pretty much mutually exclusive. Also, having to wait several lifetimes to get time off for good behavior seemed to be carrying delayed gratification a bit far. So Other Pathways were invented (calling them "shortcuts" is sooo rude). Meditating, giving alms to the poor, particularly poor and even not-so-poor, monks, endowing monasteries, also worked. The object became to meditate until one reached a hair short of nirvana, but hesitated at the last moment, thus becoming a bodhisattva. The bodhisattva deferred the final winking out of existence so that his body would remain as a visible evidence of the reality of the process, a reminder of the way to nirvana for all to see. They deferred their own final gratification and fulfillment out of compassion for the rest of the beings still suffering on the wheel of existence. Suggesting it was also a cover story for the fact that nobody was ever seen to wink out of existence, is generally considered in poor taste -- which is why I brought it up. Otherwise you might mistakenly think you were just seeing some old fart in a loin cloth sitting around doing nothing.
Theravada ('thunderbolt') is practiced in Tibet and Mongolia. It is what happens when ignorant backward peoples are exposed to a sophisticated religion like Buddhism. First, it never occurs to them to drop their worship of spirits and demons and a million petty gods and godlings. They just add a few Buddhist noises to their mass of superstitions and folk idiocies. Second, nobody worries about doing good works and meditating when you are chasing your yak across the steppe and the Huns will be here any minute. In any case enlightenment and nirvana weren't what you wanted anyway. You need somebody to pray to to save you from the Huns and to protect your yak from hoof-and-tohkes disease. Including primitive garbage in a religion is called syncretism. Tibetan Buddhism is a syncretic religion. The thunderbolt refers to a response to the inconvenience of having to meditate and think and pray and generally go to a lot of trouble. The plan is that if you perform pointless rituals and give food offerings to the gods, they may, just may, and just for the hell of it, send you to nirvana right now, all-expenses-paid. There are those who call this the Lotto school of Buddhism. Actually, again, I am the only one who calls it that.
And that's the name of that tune.