Definition from Wiktionary, the free dictionary
See also hb
Abbreviation 1 
Abbreviation of Hansestadt Bremen (Hanseatic city of Bremen). Those letters are used on the plates of the cars registered in Bremen. They are also used informally in emails or texts.
Related terms 
Abbreviation 2 
- hard black (describing a pencil that makes lighter marks than a grade B, but darker marks than a grade H pencil.)
Abbreviation 3 
- hot babe, target of seduction by pickup artists. Usually followed by a number in the 1-10 scale of physical beauty, from HB7 to HB10.