In India a duplex property unit is a house with living space divided into 2 floor .
Typically one bedroom plus kitchen, one bathroom and living / dining room on lower level and balance bedrooms and bathrooms on upper level along with any storage / recreational spaces if any. Balconies can be on both levels .
There could be terrace also if the upper level is the last floor of building.
When the word duplex is used, It is mostly for DDA flat type of properties.
These are multistory group housing flats .
Duplex units are typically old constructions 15-20 yrs old structure which could be old/raw or renovated units.
In India the duplex is not a multi family unit as in western countries like USA / Canada