Committed Relationships

I have been thinking recently about relationship status. In my worldview there are five different relationship categories:

single
betrothed
married
widowed
divorced

However, in many surveys and such an additional relationship status is offered:

committed relationship

I am not sure what this means exactly. I understand dating exclusively, but since you are not yet married or betrothed, serious dating relationships are still comprised of two single people. Plus, I find the word "committed" to be vague and, quite frankly, rediculous. So, you haven't pledged life-long fidelity to one another, so "committed" means what? Committed until someone better comes along, until we have a huge blow-out and break up, until we tire of one another? Marriage promises "until death do us part;" what does a "committed relationship" imply?