Below are listings of power cord manufacturing industry jargon and their meanings. The top two sections are regarding the styles and markings for power cord wires and the bottom section is general terms. We are always available to you through email or call 8 - 5, M - F PST.

 
Letter Definition
D dry
H heater style
J Junior service (up to 300V, if J is not listed in the wire type, then it is rated to 600V)
N neoprene
NI 'non-integral', means inner wire insulation and outer jacket are separate
O oil resistant compound used in wire jacket
P parallel
R round construction
S Service (also stranded copper wire. Designated for heavy duty insulated portable cord)
T thermoplastic
V vacuum (flexible wire initially used for vacuum cleaner applications but now widely used in many applications)
W weather resistant compound used in wire jacket (outdoor use designation to mean moisture and sunlight resistant)