There are 5 main stats: Max HP, Attack, Defense, Magic and Skill. All 5 attributes of a hero can be increased through means of Promotion, Boosting, and Leveling.
There are also 3 secondary stats: Accuracy, Dodge, and Crit. These stats are calculated as a percentage.
A Hero's Equipment also affects their stats, although this can be an increase or decrease. A good example is the Black Iron Helm, which postively affects Defense and negatively affects Accuracy.
HP is a two letter designation for Hit Points or Health Points. Characters lose HP when they take damage in battle.
The amount of Max HP is also the highest up to which a hero can be shielded.
A Hero's Attack stat determines the offensive power of any basic attack (i.e. even a Wizard's standard attack action). Most basic and skill-based attacks use this stat to determine their initial strength.
It is countered by the Defense stat.
The Defense of a hero determines how strong your Hero is against physical damage. Magic type attacks ignore the Defense stat.
The Magic stat of a Hero affects two different things: the defensive strength of your Hero against magic-based attacks and the strength of your Hero's shielding spells. Physical type attacks ignore the Magic stat.
The Skill stat of a Hero affects the in-battle Accuracy, Crit, and Dodge chance in combat.
Skill is comapared in-battle between two characters engaged in an attack. The character with higher Skill will have a better chance to dodge incoming attacks, and to land outgoing attacks - or criticals - on the enemy.
Accuracy (or Hit) is the percentage chance to land attacks during battle.
Height gives a bonus to damage and hit chance for every height unit above the target. The higher up you are, the more damage and the more guaranteed your chance to hit.
Critical Chance (a.k.a. Crit) is the percentage chance to deal extra damage(and sometimes additional effect) during an attack.
The percentage of Dodge determines the Hero's chance to avoid attacks from enemies.