C/N is Constructors number. A bit like the number of the aircraft to roll off the construction line. Assigned to every aircraft by the manufacturer.
CRM - Crew Resource management, or Cockpit Resource Management as is sometimes badly referred to. This is the notion that everybody pitches in flying the aircraft and that no-one's opinion is discounted, and everybody can have that warm fuzzy feeling that they are useful on the aircraft and all be happy and hold hands, or even sing songs. Ok, maybe not.
747BM? No idea.
747SCD, Side Cargo Door. This is a large cargo door on the side of the upper fuselage allowing large pieces of cargo and palettes to be loaded on the main deck. This appear on all combi or freighter aircraft, or even pax aircraft that can be converted quickly to a freighter.