“By Acclamation” can be described as an oral vote, where instead of people proclaiming their vote by traditional ballot or raised hands, all manner of noises, applause, cheers, or shouts of “yay” become substitutes. To acclaim is also to use your voice in an expression of goodwill or to approve. Nomination is to name someone, and usually refers to the act of naming someone to political office (or to run for political office). When put together, nomination by acclamation refers to naming someone to run for political office through nontraditional methods as described above.
From small elections at parent/school organizations for board positions to very big ones like nominating a candidate to run for president, nomination by acclamation may be used as an alternate method to balloting or hand count votes. It’s especially useful when almost everyone is planning to vote a certain way in any case. If a race, as between two people running for president of the parent/school organization is contentious, you wouldn’t choose this method because not all people would vote for the same candidate, though all might acclaim two people’s right to be nominated as potential candidates through acclamation. For the actual election, you’d want to have a fair race with ballots or hand counts in order to determine the winning candidate.
Of course if the race is already decided, showing a full vote is merely a matter of form. This was the case in the 2008 Democratic Primary Elections where Senator Barack Obama was the de facto nominee to run for President. Everyone knew the outcome in advance, and this allowed the Democratic Party, and Senator Hillary Clinton (Senator Obama’s opposition in the primaries) to do something demonstrating the unity of the party behind their candidate.
After a certain amount of delegate votes from various states were counted, showing that Senator Obama had the clear majority, Senator Clinton cut off the vote, moving that Senator Obama receive the nomination by acclamation. This gracious suggestion met with cheers, and signified an end to what had been a hotly contested and bitter primary election between the two senators. Nomination by acclamation was also thought necessary, since it recognized the extraordinary merit of Senator Clinton’s historic campaign, but moved the party toward reunification, with Senator Clinton demonstrating full support for Senator Obama’s candidacy.
Nomination by acclamation is not that unusual at the termination of presidential primaries. Vice presidential candidates are typically nominated by acclamation at their party’s convention. A related term is election by acclamation, used in Canada to express what occurs when a person is running for office without opposition.