Presidential vetoes are the constitutional or political rights of the president to override the congress i.e the Senate and the house of representatives by preventing their legislations or bills forwarded to him from becoming laws. This right is provided in the constitution to enable a kind of check and balance between the US government and the legislative arm of government.
When the US House of representatives deliberates and passes a bill, they forward it to the Senate for further deliberation and after it has been passed, it will be sent to the president to sign it into law. At this point, the choice to sign it is left to the president whether the bill will be signed or will not be signed. When a bill is not signed into law, it means it has been vetoed by the president.
The veto power of the president is usually use to disregard any bill that does not go in line with the aim and vision of his administration.