from what i see on the web the NOS means that they have diagnosed depression but it doesn't fit into one of the regular categories of depression. the diagnosis codes are very specific and for depression, i found these categories on the web for diagnosis codes that hospitals use:

<font size=1><ul>[*]Atypical Depression ( Clinical term )
Depression in persons who have an ability to cheer themselves up by doing certain things.
[*]Bipolar Depression ( Clinical term )
Depression with manic episode(s).
[*]Endogenous Depression
Acute Depression with no obvious cause(s).
[*]Involutional Depression
Depression that occurs in the elderly.
( Generally the same as Major Depression )
[*]Reactive Depression
Depression caused by an obvious traumatic life episode(s).
[*]Major Depression ( Clinical term )
Depression in persons who have no ability to cheer themselves up.
[*]Postpartum Depression
Depression that occurs in women soon after having a baby.
( Generally the same as Major Depression )
[*]Primary Depression
Depression alone with no other medical illness / disorder.
[*]Psychotic Depression ( Clinical term )
Depression accompanied by delusions and/or hallucinations.
[*]Secondary Depression
Depression that occurs after the onset of another medical illness / disorder.
[*]Unipolar Depression
Depression with no manic episode.[/list]</font>

So they are saying that they couldn't put your diagnosis into any of those specific categories based on the criteria that define them. Your symptoms may have indicated several of the categories.

I found this info at http://www.psyweb.com/Mdisord/moodd.html, and http://www.idexter.com