Classic or non-classic
While large-scale trekking started in the 1970s in Nepal, most people tend to stick to the classic routes - the Annapurna Circuit, Annapurna Base Camp, Everest Base Camp, the Khumbu (Everest) region. These routes are extremely well-travelled. Whether you use them or take your own tents, there are lodges (called 'teahouses') and villages all along the way here, and a core local population for whom trekkers are no surprise. The Annapurna circuit is sometimes even called the Apple Pie trail because industrious locals have put the thriving apple orchards to good use, preparing excellent baked desserts.
The non-classic routes involve going off the beaten track, whether further east to Kanchenjunga or Manaslu base camps, or west to Shey Phoksumdo National Park, with its magical Rara lake. On these trips you walk through much more remote country - the villages will by no means have tourist-standard accommodation or anything but the most basic local food, there are far fewer signs of development, and while most trekking areas in Nepal are rugged, many non-classic routes are especially wild west-looking. To trek these routes it is essential to carry in all your supplies, tents etc.
There are advantages to both kinds of treks - it depends on how far away from it all you want to get, how ready you are, and how many amenities you want to give up in exchange. It is a good rule of thumb to think about how we - and many others in the business - classify treks. We use a combination of altitude gained and ruggedness of terrain and trails to make our determination.