Want to go on a trek through the mountains? Make sure you have good shoes, drinking water, and snacks. A trek is a long and difficult journey.
The word trek implies an extended trip that is hard — a climb up a mountain or a journey through dense forests. In the movies and TV shows called "Star Trek," the crew of the Enterprise is on a journey through space that will last a long time. You wouldn't say that you took a trek to the corner grocery unless you had to fight through three feet of snow to get there.