To lop is to cut a chunk of something off. You could lop off your long hair, or lop off the top of a Christmas tree to make it fit in your living room.
You can physically lop things, like when you lop the brown branches off of your ailing rose bush or lop off the bottoms of your jeans to make shorts. There is a figurative way to lop too, as when an editor decides to lop the ending off a story. Or, if you choose to drive to work instead of riding your bike, you can lop an hour off the time it takes to get there.