Terminology
As currently (2008) understood in the United States, a civil union is a legally recognized status almost identical to marriage, whereas domestic partnership often connotes a lesser status that may or may not be recognized by local law. However, the terminology is still evolving; the exact level of rights and responsibilities of domestic partnership depends on the particular law of a given jurisdiction.
Since 1999, the West Coast states of California, Oregon, Washington, and Nevada have all passed domestic partnership statutes; in contrast, most legislatures in the New England region and New Jersey have preferred the term civil unions. However, as a result of the 1996 federal Defense of Marriage Act, a state may decline to recognize same sex marriages performed in other jurisdictions.
In many other countries, the equivalent legal status is referred to as registered partnership, and domestic partnership refers to cohabitation, rather than a legal status.
Read more about this topic: Domestic Partnership In The United States