WAG means Wide Gauge's(W) AC charged(A) and Freight-dedicated(G-Goods) locomotives.
"Freight-dedicated" means it is exclusively meant for Goods Train only.
WAM means Wide Gauge's(W) AC charged(A) and Mixed Load(M) locomotives.
"Mixed Load" means capable of hauling both Passenger and Freight ,it is manufactured in such a way so that it can haul both Passenger and Freight.
Same...
more... Logic is applicable for WDM which means Wide Gauge's(W) Diesel Powered(D) and Mixed Load(M) locomotives it is also manufactured in such a way so that it can haul both Passenger and Freight.
WAP means Wide Gauge's(W) AC charged(A) and Passenger(P) locomotives means it is exclusively meant for Passenger, Mail/Exp only.
Please note that the term "Wide Gauge" means "Broad Gauge" here.
If you use WAP in frieght or WAG in Passenger it will affect the "Performance" of the concerned Loco adversely.
However in IR who cares these Principles?
All thinks about the "Optimum Usage" only but hardly anyone thinks about these major Technical aspects of the "Rolling Stock" of IR i.e Locomotives.