What is a "Civil Union" and how does it differ from "Marriage"?

Something often lost in the Same-Sex Marriage debate, is the question of what exactly a so-called "Civil Union" is. FactCheck.Org has up a great article that lays out exactly what he difference is, and why it is too much for some and not enough for others.

Other federal areas in which couples in civil unions don't have the same rights as married couples include immigration (a partner who's a foreign national can't become an American by entering into a civil union with someone) and veterans' and military benefits (only opposite-sex spouses have a right to pensions, compensation for service-related deaths, medical care, housing and the right to burial in veterans’ cemeteries). Gay couples, however, may actually benefit when applying for programs such as Medicaid or government housing that require low-income eligibility. A spouse’s income is included in such applications, but a same-sex partner’s income is not.

Very interesting and enlightening. It may change my opinion about which is the right way to go on this issue.