Union Government
If a Bill passed by one House is rejected by the other, or the Houses finally disagree on amendments, or six months pass without the other House passing it, the President may summon both Houses to a joint sitting to deliberate and vote on the Bill together (this does not apply to Money Bills). If passed by a majority of the total members of both Houses present and voting at the joint sitting, the Bill is deemed passed by both Houses, subject to specific rules limiting what amendments can be proposed at that joint sitting.
This is the constitutional deadlock-breaking mechanism: if the Lok Sabha and Rajya Sabha genuinely cannot agree on a non-Money Bill, the President can call a joint sitting of both Houses together, where a simple majority of all members present (combining both Houses) can pass the Bill - effectively letting the larger Lok Sabha's numbers usually prevail in such joint sittings, since it has more members than the Rajya Sabha.
A joint sitting of Parliament has been used only rarely in India's history - for example, to pass the Dowry Prohibition Act (1961), the Banking Service Commission (Repeal) Bill (1978), and the Prevention of Terrorism Bill (2002) - precisely because it's meant to resolve a genuine, prolonged deadlock between the two Houses, not routine disagreement.