[King's Gambit]

As a total beginner to the subject matter of 'Trains' my wife bought me a copy of the Book "Traction recognition" by Colin Marsden. However I am having problems understanding several things, and obviously I am in need of some help. So, can somebody explain to me what the following mean? DMCL, MSL, DMCL, DMS, MS, there are quite a few more, probably to many to list. So I ask can anybody out there help me with this.

I thank you in advance for your help in this matter.

Cheers.

Stuart. (King's Gambit)