Down is from Headquarters (the division the train belongs)
Up is towards Headquarters (the division the train belongs)

e.g:- 06527 Down Banglore-New Delhi Karnataka belongs to South Western Division, hence it is Down, and its pair i.e 06528 Up New Delhi - Banglore Karnataka Exp is going towards its headquater i.e Banglore hence it is Up
...
more...

Members, Moderator plz correct me, if I am wrong

The UP and DOWN numbering of trains are depended on the zones operating and not on the direction in which train travels. Intermediate trains which doesn’t originate from the headquarters follows numbering based on the direction of away/towards the headquarters.

Generally the tracks moving away from headquarters are DOWN and the converse for up tracks. A train on the down track is has a DOWN tag attached (like 16501 Down) to its number and converse for the reciprocal 16502 up.
...
more...

When the zones change, the tracks may rejigs their Up and Down status, the trains follow suit and change the up and down in their names as well..so when the 16502 arrives at Daund, it is a Up train. However when it departs Daund for Ahmedabad, it now rides on the Down tracks of the Central Railways like 11077/12129 and many more..!!