The word superdelegate becomes common vocabulary during election times, especially as political parties prepare to nominate their candidates for the United States presidency. These "super" elected officials or party leaders have special privileges during presidential nominating conventions.
Every four years, the Democratic and Republican Parties hold big national conventions to determine their nominee to run for president. At the convention, state delegates vote for their respective party candidates, with each convention winner going on to compete in the general election as their party's nominee.
Before the nominating convention can happen, though, each state holds primary elections or caucuses (open community meetings) to designate each party's convention representatives — or pledged delegates — who will be seated at the convention. These pledged delegates vote at the convention for candidates who are running for their party's nomination. (A pledged delegate must vote for a specific candidate at the convention, at least in first-round voting.)
Defining differences between pledged delegates and unpledged delegates
Before the primaries and/or caucuses are held, each state is allocated a total number of possible pledged delegates that can be sent to the national convention. Pledged delegate numbers for each state are generally based on the percentage of votes granted in the Electoral College. (Electors in the Electoral College are proportional to its number of Representatives and Senators in the United States Congress.)
In addition to these pledged delegates, each party bestows "unpledged" delegate status on all party officials as well as present or former office holders. These unpledged delegates are seated at the conventions with no strings attached, and can vote for anybody they want, any time they want during the convention. Democrats call these folks superdelegates. Republicans usually just call them unpledged delegates.
What superdelegates mean to the Democratic party
In the Democratic Party nominating process, each state's pledged delegates are divvied up according to a ratio of their candidates' portions of the popular vote during the state primary or caucus. For example, say a state has 100 total potential pledged Democratic delegates. In the primary, a total of 4,000 votes are cast. Candidate "A" gets 1,000 votes, and candidate "B" gets 3,000 votes. Based on a proportional ratio of the overall Democratic votes in that state, candidate "A" wins 25 pledged state delegates to the convention, and Candidate "B" wins 75. Quite often, this process of proportional allotment of delegates opens the door to a close race for the Democratic nomination.
And that's where the real power of the superdelegates can come into play. Since superdelegates are unpledged at the convention, a big block of superdelegate votes at the last minute can sometimes push a candidate over the top to win the delegate count overall, and thus the nomination, even if the other candidate had won the popular vote in state primary/caucus elections.
What unpledged delegates mean to the Republican party
In the Republican Party process, typically, the winner of the majority vote at state primaries and caucuses receives all of the pledged delegates for each state they win. Using the voting scenario from the Democratic example, Republican candidate "A" would get 0 pledged delegates to the Republican convention, and candidate "B" would get 100. This process makes for a much faster nominating process, and doesn't often result in a close race at the convention. As a result, unpledged Republican delegates seldom need to use their "super powers" at their convention.