Some well-known examples of initiatives are various ballot measures or propositions enacted by voters in states such as Oregon and California, such as California Proposition 13 (1978), which limited real estate tax rates.
An initiative is distinguished from a referendum in that a referendum is submitted to voters by a vote of a legislature, while an initiative can be placed on the ballot in another way, often by obtaining a sufficient number of signatures on a petition. The availability, if any, of an initiative or referendum process varies from state to state (or political jurisdiction).
See also: recall.