Class is the term used to indicate your character's profession. There are currently 13 classes in the game and they fall under 6 genres. Augurers, Mages, and Nephandi are Sorcerers. Clerics are Divinity. Bladesingers, Fathomers, and Thieves are Rogues. Paladins, Rangers, Warriors and Barbarians are Fighters. Vampiress are Aberrants. Druids are Shamans.
Class determines one's choice of skills and primary, secondary and deficient stats. It also affects hitpoints, mana, fighting abilities and experience points per level. It will restrict which deities you can worship and which guilds you can join.
Character choice affects the base stat rolls. Fighters (Barbarians, Paladins, Rangers and Warriors get 3 added to their strength, Mages and Nephandi) get +3 intelligence, Rogues (Bladesingers, Thieves, Fathomers) and Vampires get +3 dexterity, and Clerics, Druids and Augurers get +3 wisdom. For example, a Human, being the race with no initial stat bonuses, would have almost a 50% chance to roll a 13 or 14 for any given stat. But depending on the class you choose, one stat would roll a 16 or 17 about half of the time.
Bladesinger is the only class which is deadly only, meaning players intending to be peaceful cannot play this class. Barbarians cannot choose to be deadly initially, however they can switch at a later point.