A veto – Latin for "I forbid" – is the power (used by an officer of the state, for example) to unilaterally stop an official action. This is applicable especially the enactment of legislation. A veto can be absolute or limited.
For instance in the United Nations Security Council, the veto power of permanent members of the council is absolute. The permanent members of United Nations Security Council are China, France, Russia, United Kingdom, United States of America. In the Security Council it’s e permanent members can block any resolution.
Veto can be limited, as in the legislative process of the United States, where a two-thirds vote in both the House and Senate may override a Presidential veto of legislation.
A veto only gives power to stop changes, not to adopt them (except for the rare "amendatory veto"). Thus a veto allows its holder to protect the status quo.
The concept of a veto body originated with the Roman consuls and tribunes. Either of the two consuls holding office in a given year could block a military or civil decision by the other; any tribune had the power to unilaterally block legislation passed by the Roman Senate.
In India, the president has three veto powers i.e. absolute, suspension & pocket. The president can send the bill back to parliament for changes, which constitutes a limited veto that can be overridden by a simple majority. The president can also take no action indefinitely on a bill, sometimes referred to as a pocket veto.The president can refuse to assent, which constitutes an absolute veto.