It looks a lot like a _African sacred ibis_ ( _Threskiornis aethiopicus_ ) (wikilink). However, given your location in India, the closely related _Black-headed ibis_ (which some consider to be part of the same species) might be more likely.
The _African sacred ibis_ is native to mainly sub-saharan Africa, but is considered Invasive in some parts of the world (inkl. Europe and parts of Asia). The _Black-headed ibis_ is however a native breeding bird to large parts of Asia (inkl. India), which makes this more likely.
