Sharp and Galloping refer to the the severity of the bends.
Courses such as Exeter, Haydock and Hexham can be considered to be galloping tracks whereas Fakenham, Cartmel and Plumpton can be called sharp or tight.
Easy and stiff will refer to the inclination of the finish. If a course has a flat or downhill finish (Haydock, Kempton, Brighton) then that would be easy whilst courses with an uphill finish (Sandown, Cheltenham, Exeter) would be considered to be stiff.
That’s my understanding of the terms although I’m sure somebody will be able to correct me if I’m wrong.
Hope this helps.