It means running a train with the spare coaches of various trains.
It is rescheduled because lazy GHY folks are very slow in formation of rakes.
Earlier my college was adjacent to GHY Coaching Depot, I have experienced it. This is the reason why trains like GHY - Barmer, GHY - OKHA always depart GHY behind schedule.
In comparision the south bound trains...
more... like GHY SBC, GHY TVC etc. are maintained by NGC (New Guwahati) base near GHY, they are maintained good compared to GHY CD.
I think one can notice that the trains from GHY base do not have any fixed structure.
I am afraid that some day these lazy folks will place pantry car between General Coaches :-)