Originally described only a specific person. But, the word has long since been extended to describe an indefinite concept that can be applied to most anything. It is especially appropriate when there is doofiness involved that one wishes to portray in a positive light. The first syllable can also be extracted and used as a prefix to any other word to confer upon it the zen of zwerdog.
Buying three family-size frozen lasagnas and four whole rotisserie chickens for the week's groceries is a very zwerdog-like thing to do.
The zwer-popotamus would be the most amazing animal on the planet.