A Class is a type of role denoting a PC's capabilities within combat scenarios. Classes provide HP values, Initiative, Acrobatics, trainings, and an ability. As with other roles, it also provides a set of cards that can be selected for building a deck for combat.
The selected Class specifically reflects the battle training and fighting style of the PC. While some PCs may have found employment and social status as a result of these skills, this would tend to be the exception rather than the norm, at least prior to beginning an adventuring career.