The title pretty much says it all. I looked up the definition, and it seems to serve the same purpose as a primary. Is there a difference?
Does this help?
A primary is an election – you cast your vote on your party’s ballot and go home. The votes determine which delegates go to the national convention.
A caucus is a far more involved affair, consisting of people dividing themselves into groups for each candidate, courting undecided voters and giving speeches and so forth. In Iowa, at the end of the caucus, the number of people who place themselves in each candidate’s group determine which delegates attend the county conventions, which then elect delegates to a state convention, which then elects delegates to the national convention.
Two big differences influence their outcomes.
In a caucus, everybody knows how you are “voting”.
And in a caucus, you can adjust your “vote” according to how others “vote”. So it’s more like reaching a concensus.
To take a pathological case, say there are 5 candidates with almost no differences between them, and one candidate who is radically different. And suppose 2/3 of the electorate agree the radical candidate would be disastrous but 1/3 like that candidate.
In a primary you might expect 2/3 of the vote to be spread amongst the 5 indistinguishable candidates, and 1/3 would go to the disastrous candidate. Thus, at the end, 2/3 of the electorate, who would have been satisfied with any of the other choices, think the election was disastrous.
In a caucus, one of the nondisastrous candidates would win.
What’s a black caucus?
If a Primary sees it’s shadow, we’ll have six more weeks of winter. A caucus is stuff you use to seal up a leaking window pane.
This is a slightly different use of the word “caucus” which refers to informal groups of legislators aligned for a particular cultural similarity or legislative agenda. (See congressional caucus.) The Congressional Black Caucus is a group of black Senators and Representatives who meet to discuss issues affecting black people at the federal level. Many state legislatures also have black caucuses.
Not necessarily.
Keep in mind that there can be different types of caucus, too. In Iowa, the Dems do the physical caucus thing, where you group together and go thru several rounds of elimination. Everyone knows how you’re voting in that system. The Pubs just take a type of “straw poll”, and they do vote in secret.
Not everybody’s vote necessarily counts in a caucus.
The Democrats in Iowa are electing about 2500 representatives who will vote later to determine who gets the delegates to the Democratic convention. Each caucus elects a set number of these reps.
Say that a certain caucus will elect 5 reps. The caucus votes among all the candidates. But any candidate who gets less than 15% of the vote in the room is excluded. That candidate’s supporters can then go to their second choice. (Or they can drop out at that point.) The process is repeated until everyone left has more than 15% of the total. Those votes are allocated among the 5 reps.
Weird as this seems, it’s actually a form of the second choice balloting that people sometimes argue about in threads here to change the voting system to some sort of proportional representation.
A primary is a simple vote once, total them up, allocate system. They are very different.
The real difference is that a Primary is almost always won by a candidate who spends the most money on 30-second TV commercials. A Caucus is won by a candidate who has the most volunteers willing to go to the caucus meeting in their neighborhood and speak for that candidate.
(That’s why you frequently see editorials by TV & Newspapers pushing for a Primary system – they could sell a lot more ads!)
A candidate who has lots of enthusiastic supporters but little money can win in a Caucus system; but hardly ever in a Primary.
It actually reminds me of the “Australian ballot” used in Hugo and Nebula award voting.
I’ll have to dig up John Barnes analysis of voting systems that lists the pros and cons of each method.
While this used to be largely true, in this particular case Obama outspent all other candidates, including, by a wide margin, Mitt Romney who was accused of trying to “buy” votes. Even Hillary Clinton spent more than Romney according to some news organizations.
In modern America you need both ads and volunteers and that’s true both in primary and in caucus states.
[True story]
I was taking a Political Science class in high school, when the subject of the day came to caucuses–pretty much they were described as friedo mentioned: a group of politicians aligned along a particular political aim.
Teacher: So, can anyone tell me of any caucuses they know?
Student 1: The Black Caucus?
Teacher: Very good! Anyone else?
. . .
. . .
::crickets chirping::
. . .
. . .
. . . and one football player-type raises his hand sheepishly.
Student 2: Um . . . Seacaucus?
. . .
. . .
. . . immediate, explosive laughter from the rest of the class.
Teacher: In twenty seven years of teaching, nobody has ever brought that one up. You get an “A” on today’s surprise quiz. 
[/True Story]
Tripler
Aaaah, the benefits of being reared in New Jersey.