Of the dinosaur tracks that people find in the outdoors, there are two main types, true tracks and natural casts (there are also undertracks and infills but these are harder to see).
What exactly is the difference between these two types of dinosaur tracks?
The easy way to think of this is that tracks left in concrete sidewalks are true tracks while pouring plaster of paris into animals tracks left in mud would results in a cast.
Sometimes the dinosaur tracks were made in materials that turned to stone and were then preserved as true tracks, and sometimes the tracks were made in soft materials and then filled in with other materials that turned to stone and the only the cast is preserved.
The standard diagram explaining this is,
For further reading I would suggest these resources,
Also, the track in my other question is a natural cast.