"Class" means the category of chocolate. They bars I review are grouped by Class to allow for more meaningful ratings between similar types of chocolate. Depending on my mood and what flavor I'm interested in I'll know what it the best in each Class.
The Classes I use are:
Dark (subdivided into 50s, 60s, 70s, 80s, 90s, 100)
See the subpages below for more specific ratings summaries by Class. They're also all summarized in the file "Ratings by Class".