Trekking is not a mountaineering. For mountaineering, there are 8 out of 10 most highest peaks in the world in Nepal. However the trekking around or below these mountains are very popular. The trekking in Nepal is a simple walking trip along trails hill road in the mountains.
Many of such roads have been used for every day travel and trade for many years. A trekking trip can be of any length one can choose from a hiking to one month long trek. However a hiking in Nepal is a mini trek in Nepal. You trek one day along the rim of Kathmandu valley or Pokhara Valley, dine and rest in a comfortable to luxurious resort, and next day walk or drive back to city after breakfast. There are many popular mini treks around Kathmandu and Pokhara valley, which you can complete in one night two days, where as there are various longer treks around Annapurna and Everest region lasting from a week to a month.