A nominee is someone whose name has been put up for election, whether on a formal ballot or in a less formal voice vote among a group of people.
In smaller groups, nominations are made for a position (such as chair of a committee), and if seconded the nominee is added to the candidate list. Nominations are closed by a movement, seconding, and general vote. Then a vote, either by voice or secret ballot, is conducted to determine the winner.
In larger, more formal elections, nominations for the ballot are usually decided by political parties (both major and minor). The most visible form of this in American politics are the quadrennial nominating conventions of the Democratic and Republican parties, where the party's choices of candidates, determined via the primary process are presented to the people, during week-long, carefully scripted and widely televised celebrations.