With car insurance, the physical damage coverage of collision insurance typically covers damage to your automobile cause by a collision with another vehicle or object -- or the upset set of your vehicle.
Insurance companies' definitions of upset vary depending upon the company's internal guidelines and policy terms; however, in general, upset of a vehicle means if it was caused to tip or turn over. So if you roll your vehicle down an embankment, then that is usually classified as upset of the vehicle.
If your vehicle flips over and hits a tree, this would be a collision claim due to both the upset of your vehicle and the collision with the tree. But your car doesn't have to collide with anything for your collision insurance to be used. Running off the road and the car tipping over due to the slope of the ground and being damaged would fall under the upset portion of your collision insurance coverage.
Comprehensive coverage is the other physical damage coverage. Loss caused by missiles, falling objects, fire, theft or larceny, explosion, earthquake, windstorm, hail, water, flood, malicious mischief or vandalism, riot or civil commotion, colliding with a bird or animal, or breakage of glass are other than collision losses and thus claims for these incidents would fall under your comprehensive coverage.
To find out how your insurance provider defines upset as part of a collision loss, read through your policy and speak to your agent if you need clarification about anything.