What Ed said is correct. A trek is a type of hike, that is long and difficult. Hike example: "We are going on a 5 hour hike." Trek example: "We are going on a week-long trek through the mountains." Also, a trek usually means you end at a different location than you begin. Hike example: "After 3 days of hiking, we returned to the base camp." Trek example: "After a month-long trek, we finally arrived in Washington state."

I think trek is used for longer trips: A trek through Africa. A trek across the desert. It also is usually a difficult trip, usually in a remote or wild location. A hike can be much shorter, and is always on foot: We are going for a 5-mile hike in the Smoky Mountains. It is not as difficult as a trek. You can hike in a state park near your home, but you wouldn't trek through a state park near home. I hope this helps a bit.