Exactly what constitutes a "neck beard"?

[Portasaurus]

Calling someone a "neck beard" has to be one of the top 10 all-time favorite insults in this community. As such, I'd like to understand it a bit more.

If I grow a full beard -- including the neck part -- does that count as having a neck beard?

Or is a neck beard when the beard is ONLY on the neck and nowhere else on the face?

Are there maybe some pictures or gifs available on the internet which might help illustrate the difference?

Thanks!