Nepali is an Indo-Aryan language spoken in Sikkim, Nepal, Bhutan, and some parts of India and Burma. It is the official language of Nepal. Roughly half the population of Nepal speaks Nepali as a mother tongue, and many other Nepalese speak it as a second language.
Nepali goes by various names. English speakers generally call it Nepali or Nepalese (i.e. the language of Nepal).
It is also called Gorkhali or Gurkhali, "the language of the Gurkhas, "and Parbatiya, "the language of the mountains." Khaskura is the oldest term, literally speech of the Khas who were rice-growing Indo-Aryan settlers in the Karnali-Bheri basin of far western Nepal since prehistoric or early historic times. Khaskura exists in opposition to Khamkura, a group of Tibeto-Burman dialects spoken by Kham peoples in highlands separating the Kharnali-Bheri basin from the Gandaki basin in central Nepal.
Then perhaps 500 years ago, Khas peoples migrated eastward, bypassing the inhospitable Kham highlands to settle in the lower valleys of the Gandaki basin suited to rice cultivation. One notable extended family settled in Gorkha, a petty principality about halfway between Pokhara and Kathmandu. Then in the late 1700s a scion named Prithvi Narayan raised an army of Gurungs, Magars and possibly other hill tribesmen and set out to conquer and consolidate dozens of petty principalities in the himalayan foothills. Since Gorkha had replaced the original Khas homeland as the center of political and military initiative, Khaskura was redubbed Gorkhali, i.e. language of the Gorkhas.
Prithvi Narayan's especially notable military achievement was conquest of the urbanized Kathmandu Valley, on the eastern rim of the Gandaki basin. This region was also called Nepal at the time. Kathmandu became Prithvi Narayan's new capital, then he and his heirs extended their domain east into the Kosi basin, north to the Tibetan Plateau, south into the plains of northern India, and west of the Karnali/Bheri basin.
Expansion, particularly to the north, west and south brought the growing state into conflict with British and Chinese territorial ambitions. This led to wars that trimmed it back to roughly Nepal's present borders or less, however both great powers understood the value of a buffer state and did not attempt to reduce the new country further. Since the Kathmandu Valley or Nepal had become the new center of political initiative, this word gradually came to refer to the entire realm and not just the Kathmandu Valley. And so Gorkhali, language of Gorkha, was again redubbed Nepa