PDD-NOS is just atypical autism. It is any kind of autism that doesn't fit into a specific subtype (Asperger's, Kanner's, CDD, or Rett syndrome). Ironically, most autism doesn't fit into a specific subtype; about sixty percent of us have PDD-NOS, though some of those people will identify as Aspies because their cases are close enough to AS to make no difference except from a diagnostic perspective.
PDD-NOS comes in all severity levels. For a diagnosis, it just has to be severe enough to cause impairment. It can be because you have too few symptoms (but the ones you have are strong enough to cause impairment), because you have symptoms of more than one subtype, because you used to qualify for one subtype but "grew out of it" (for example: Kanner's in childhood, looks like Asperger's in adulthood--common situation there, but AS is ruled out by the history of speech or self-care difficulties). You can also be diagnosed PDD-NOS because you have other disabilities that complicate diagnosis, or because you have an atypical variant of Rett's or CDD, or because your autism is secondary to something like Fragile X. It's also used for cases where there's severe global developmental delay and there's no telling what is due to autism and what is due to the overall intellectual disability.
If you have PDD-NOS, you're probably just best off calling yourself "autistic", just plain autistic... Autism is a very big category, very diverse. People are just going to have to understand that subdividing autism into smaller categories won't help us any when it comes to offering services and treatment, because there are no clear-cut subcategories, really. Any time you put an autistic person into a subcategory, you tend to lose information, not gain it, because they will almost inevitably have traits that don't fit into the subcategory, and be missing some that do.
Asperger's is probably the subtype that fits me best if you refuse to use PDD-NOS. But, unlike most people with AS, I don't have social anxiety and have a good deal of imagination. I also have many classic autistic traits: Loss of communication ability during shutdowns, being not-quite-independent, learning to take care of myself later than most people. If you assume Asperger's, you will lose the information about those particular traits. If you assume classic autism, you'll lose the fact that I am a relatively effective communicator. So PDD-NOS it is. I tend to be a little annoyed with the doctors who put "Asperger's" on my record simply because I can speak--it leads to incorrect assumptions. Heck, sometimes it leads to incorrect assumptions for people who do fit the Asperger's criteria properly; it's even worse when you don't. I have often found myself in the somewhat amusing position of having to educate the professionals about my own case.
PDD-NOS is atypical autism, or just plain autism if you don't want to be fancy about it. You're an individual--you share certain traits with the Spectrum, but your autism is expressed in a way that is not quite like anybody else's. That's true of most of us, but perhaps somewhat more so for people with PDD-NOS. I like that about the diagnosis: It reduces, at least somewhat, the chances that assumptions will be made based on my label.