NOTA stands for "None of the Above". It is also known as "against all" or a "scratch vote". It is a right given to voters that enable them to not vote for any of the candidates contesting the election if they feel that none of them is a deserving candidate. It is a way to express the dissatisfaction of not having a single candidate worth to vote for or to show that the voter does not have confidence in any of the contesting candidates.
So, it is a right of voters to reject all the candidates of a particular constituency if they feel that there is not even a single deserving candidate in their constituency. However, it does not make any significant difference in the outcome of the election results.
The supreme court of India on 27 September 2013 ruled that there should be an option as a right to register a "none of the above" vote in elections. He ordered the ECI to provide a button for the same in the electronic voting machines (EVMs). Later, after a few months, to empower such voters the Election commission of India (ECI) introduced a button for NOTA option in December 2013 in electronic voting machines. This option appears in the Electronic Voting Machine (EVM) at the end of the list of candidates. When voting was done using ballot papers, the voter, who want to use NOTA, had the choice to put the ballot paper in the box without marking against any of the candidates and the vote was counted as NOTA.
The NOTA was first used in India in 2013 in the Assembly elections held in Chhattisgarh, Mizoram, Madhya Pradesh, and Rajasthan and the Union Territory, Delhi. Over 15 lakh voters used this option in these polls. NOTA is not only used in India. There are many countries where it is practiced in the elections such as Brazil, Bangladesh, Ukraine, Colombia, Finland, Spain, Sweden, France, Belgium, Greece, and more.