Since the topic is becoming more and more relevant to the current 2016 GOP race, I'll let our good friends at CNN explain what a brokered convention is. I'll do a TL;Dr at the end for the lazier ones.

Getting a Brokered Convention:

The Republican party will assign 2,472 delegates through a state-by-state series of caucuses and primaries between February and June. To win the nomination, a given candidate requires a simple majority, or 1,237, of the total. The states holding their contests before March 15 are required by party rules to dole out their delegates proportionately, meaning 51% of the vote translates to the same percentage of the state's allotted delegates.

To further complicate the matter, there is the party's so-called "Rule 40." This bylaw, added in 2012, states that any potential nominee must "demonstrate the support of a majority of the delegates from each of eight or more states." There are, as we approach the CNN debate in Las Vegas on Tuesday, a total of 14 candidates in the mix. No fewer than 10 can reasonably expect to win a noteworthy proportion of delegates as the race extends into spring.

For example, polls have shown Trump with a durable lead in Iowa -- he's up 13 points on Ted Cruz, his closest rival, according to Monday's CNN/ORC poll -- but even then, his total support in this sprawling field is only 33%. Multiple candidates could win a majority in eight or more states, or no one could. Either way, it adds up to chaos on the convention floor. (Interestingly, the rule essentially prevents a would-be outside savior, like Mitt Romney, from parachuting into the process late, as that person would obviously arrive without those eight state majorities.)

One Republican with a full grasp of the RNC rules reached out after the story first published to point out that the eight-state requirement in Rule 40 is technically temporary. The RNC will vote on a new rule at the convention in 2016 and could again change the number of states at that time.

Contested vs. Brokered:

Simply stated, if no candidate (and this goes for both parties) finishes the primary season with majority of delegates, the summer convention can be described as "contested." The last "contested" GOP primary came in 1976, when President Gerald Ford and an insurgent conservative named Ronald Reagan arrived at Kansas City's Kemper Arena short of a clinching total. Both campaigns sought to sway or romance their way to the necessary majority, which Ford would seal just before the first floor vote.

Because that initial ballot delivered Ford the nomination, the 1976 convention is not technically considered to have been "brokered."

For that, we have to look back more than 60 years, to the 1952 Democratic contest. Tennessee Senator Estes Kefauver led the race after the last round of primary voting, but did not win the nomination after the first floor ballot. No one did. It was not until the third ballot that Adlai Stevenson, the reluctant home-state governor with the backroom backing of outgoing President Harry Truman, finally emerged with the nomination.

The most recent "brokered" convention for Republicans came four years earlier, in 1948, when they chose New York Gov. Thomas Dewey after three ballots.

Dewey, Stevenson and Ford all lost their general election contests.

Tl;Dr:

If no GOP candidate arrives to the convention with the support of 1,237 delegates and satisfying the current Rule 40, the contest becomes contested, with the candidates closest vying to win delegates who have yet to pledge support. If, after the first vote, a candidate is chosen, then it is classified as contested. If it goes to a second, third or more vote, it is a brokered convention - and becomes more complicated. Once it reaches a second vote, and is classified as brokered, all delegates are allowed to vote for any candidate on the ballot.

Important to note that in the past, candidates from a party who's convention was either contested or brokered did not win their respective general election - likely due to the fact that the party remained divided.

Icy, who do you think's going to get the nomination?

I really don't know, because this election cycle is so different from any others I've studied - fifty days away from Iowa and we still have twelve viable candidates (plus a handful of jokes) that are vying for the nomination. After the first three primaries, we'll hopefully have a better clue.

I'm still going to say Rubio, but cautiously.