Long, deep tracks made by wheels, especially in the mud or dirt.
Ruts are usually seen as a bad thing because they can make it hard to move or drive.
Examples:
The car got stuck in the ruts in the road.
The wheels made deep ruts in the soft ground.
The horse's hooves sank into the ruts in the muddy path.
The ruts in the road were so deep, it felt like a rollercoaster.
The ruts in the field were so big, you could hide in them.
The ruts in the road were like big ditches for the car to fall into.