  In 1935, Albert Einstein and two colleagues, Boris Podolsky and Nathan Rosen
(EPR) developed a thought experiment to demonstrate what they felt was a lack
of completeness in quantum mechanics. EPR also postulated the existence of more
fundamental theory where physical reality of any system would be completely
describe by the variables/states of that fundamental theory. This variable is
commonly called hidden variable and the theory is called hidden variable theory
(HVT). In 1964, John Bell proposed an empirically verifiable criterion to test
for the existence of these HVTs. He derived an inequality, which must be
satisfied by any theory that fulfill the conditions of locality and reality} He
also showed that quantum mechanics, as it violates this inequality, is
incompatible with any local-realistic theory. Later it has been shown that
Bell's inequality can be derived from different set of assumptions and it also
find applications in useful information theoretic protocols. In this review we
will discuss various foundational as well as information theoretic implications
of Bell's inequality. We will also discuss about some restricted nonlocal
feature of quantum nonlocality and elaborate the role of Uncertainty principle
and Complementarity principle in explaining this feature.
