Former Massachusetts Gov. Mitt Romney, the 2012 Republican presidential nominee, holds hands with wife Ann as he takes the stage to address supporters at his Iowa caucus night rally in Des Moines, Jan. 3, 2012. REUTERS

Iowans will head to nearly 2,000 precincts Monday for the first vote that many see as indicative of the fate of the 2016 presidential election. But don't call it a primary. Iowa holds caucuses instead. So what's the difference?

A caucus is organized by the political parties in that state, while a primary, like any official election, is run by the state government. Iowa and 12 other states hold at least partial caucuses to choose their candidates.

In primaries, people cast their ballot in secret and votes are tabulated after polls close. Caucuses are much more complicated. Both Republicans and Democrats in Iowa head to the polls at the same time to choose their party's respective nominee for president, but how the caucuses work differs for each party.

The Democratic Party: Iowa Democrats will visit one of the roughly 1,100 precincts across the state, where candidate representatives are allowed to give speeches. There, they separate into groups to announce their support of a party candidate. Groups with less than 15 percent support for a candidate are disbanded, and the members of the group are allowed to join another group or leave. Based on how many caucusgoers are in each group, a formula is used that varies from county to county to determine the winner of the party. For the first time this year, the outcome will be sent via a phone app to the state party organization. The number of delegates at county conventions are proportionally allocated based on the support at each precinct, as well. These county delegates vote for other delegates to the 29-member congressional district conventions who attend the national convention.

RCP Current Poll Average for Iowa Democratic Caucus | InsideGov

The Republican Party: Like Democratic caucuses in the state, GOP-candidate representatives also kick off the night by giving speeches to woo voters at the precincts. Following the speeches, a straw poll is taken and the results are sent to the Republican Party of Iowa. The results will also be sent using an app for Republicans for the first time. The candidate with the plurality of votes in Iowa wins the caucus, as announced by state party officials. Unlike the Democrats, the caucusgoers then weigh in on the party platform through a vote. For caucusgoers, the night's final business is when they elect delegates to the county conventions in March. These county delegates later elect national delegates to attend the national convention, where they vote proportionally to the Iowa Caucus straw poll.

RCP Current Poll Average for Iowa Republican Caucus | InsideGov

To see the results of the 2016 Iowa caucuses, visit the Des Moines Register's coverage here.