All these acronyms are related to the toe and arch protection for all types of combat boots. Some boots have reinforced protection for your toes, and some do not.
Anyway, MT means that the toe of the boot has a steel shell which guarantees maximum protection against heavy objects. CT indicates a lighter material (usually composite) that offers enhanced toe protection.
SP refers to a puncture-resistant steel toe sole while CP refers to the same properties, but with more lightweight materials.