A coulee is like a big ditch that's carved into the ground. It usually happens in places where there used to be water or where there is still water.
When it rains or snow melts, water moves and sometimes it can carry a lot of dirt and rocks with it. Over time, this can make a big difference in the land. It can create a long, narrow valley with steep sides, which is called a coulee.
Some coulees are made by rivers or streams that slowly move and wear down the land over time. Others are made by sudden bursts of water, like when a dam breaks or a flash flood happens.
People who live near coulees often enjoy exploring them, because they can be full of interesting rocks, plants, and animals. Some people even build their homes near coulees, because they like the way the land looks and feels.
But it's important to be careful around coulees, because they can be dangerous too. If you're walking or playing near a coulee, make sure you stay away from the edges, and always listen to adults who tell you to be careful.