From HELP CLASS...
Code:
Mercenary -- the basic warrior profession
Swashbuckler -- skilled in swift multi-handed strikes
Barbarian -- uncivilized warrior of brute force
Priest -- the basic clerical vocation
Paladin -- knight blessed by the gods of light
Hellion -- knight blessed by the gods of darkness
Shaman -- uncivilized cleric with spiritual powers
Rogue -- the basic adventuring profession
Scout -- skilled in woodlore and bush-fighting
Bard -- performer and minor magician
Sorceror -- the basic wizard profession
Warlock -- worships and uses the elemental powers
Necromancer -- diabolical master of the undead
From the above, you should get a fair idea of the IC nature of each class. I'm not quite sure how much more you'd need to know to match your character concept up with the right class. On MUDs with some of the more fancy class names (Auriger, or something??), then I can understand more information should be given because the name isn't very well known.