Plural of referendum, although referendums is certainly also acceptably used as an alternative plural.*

Referenda are direct polls of a democratic electorate, requesting their input on a specific question of policy. In the United States, voter referenda are one of the few ways, along with jury service, that the individual citizen is empowered to participate directly in the decisionmaking processes of government. That's because most governing systems called "democracies" are actually representative democracies, so the true day-to-day decisionmakers are not the citizens, but rather, their official, elected representatives.

Referenda serve as a citizen check on the power of elected officials, since any individual citizen can, in most U.S. jurisdictions, bring any matter before the voting-public-at-large in the form of referenda, provided that (s)he is willing to put in all the effort of gathering enough signatures.

Referenda are not likely to be successful, though, unless the referendum effort is paralleled by a campaign to educate the voters on the issues. For special referenda elections (even more so than for any other election), citizens simply will not show up at the polls if they don't care about the outcome.

*To English purists who would insist on the "incorrectness" of pluralizing referendum as referendums:

Referendum is an English word, spoken by speakers of English, not Latin. It is the body of modern English speakers that is empowered to decide -- through actual practice -- how to pluralize English words. Linguistic correctness is a de facto standard. Indeed, nearly every word in the French language is a bastardization of a Latin word. (Maybe French is regarded as legitimate because they make such good wine.
But irregardless [sic] of that . . .)