Referendum

Ballot initiatives
Ballot measures
Initiative and referendum
Initiatives, Ballot
Propositions (Referendum)
Referenda
Referendums

Yount, P.J. Measure 9 : Oregon's 1992 anti-gay initiative, 1997: leaf 1 (measure on the ballot) leaf 4 (initiatives; ballot measure)
Wikipedia, Nov. 4, 2005 (a referendum (plural: referendums or referenda) or plebiscite is a direct vote in which an entire electorate is asked to either accept or reject a particular proposal; certain kinds of referendums are referred to as: ballot measures or propositions)
Ballot initiatives : the ins and outs of getting an initiative on the California ballot, 1999.
Google search, Dec. 4, 2014 (438,000 hits on "ballot initiatives")