NOTA (None Of The Above) is an option in election Ballot (Paper or Electronic) to exercise your right of saying ‘I don’t like any of the contesting candidates and don’t want to vote for any of them’.
Before 2009 under 49-O, a voter can inform Presiding Officer that he doesn’t wish to vote for any candidate and an entry used to do in a register with voter’s signature/thumb impression.
There were few issues with this, 1. It was not anonymous 2. Very few people knew about it 3. Those who knew did not use it much due to hassles.
To solve these problems in 2009, Election Commission under the guidance of Honourable Supreme Court of India introduced NOTA in the ballot.
Long-term is when people will start increasingly vote in favour of NOTA when none of the candidates deserves, then Election Commission/Govt/Court will take a note of it and we should see some good changes in favour of NOTA (may be election becomes void if NOTA gets the highest vote)