One common design in MMORPGs is the "holy trinity" of class roles: Tank, Healer, and DPS (or damage dealers). As most games are about combat, these roles are about how damage is handled: Tanks can mitigate incoming damage from enemies, healers restore damage done from enemies, and DPS classes do damage to enemies. 
"crowd control" (CC) classes can temporarily take enemies out of the combat, and "buffer" classes can use abilities that enhance the abilities of other classes.
The DPS role sometimes has specialized categories: melee, ranged, single-target, area of effect (AoE), etc.
- Fighting Man (renamed "Fighter" in later editions), focused on combat abilities, but almost entirely lacking in magical abilities
- Magic User (renamed "Mage" and then "Wizard" in later editions), featuring powerful magical abilities, but physically weak
- Cleric, specializing in healing and supportive magical abilities
- Thief (renamed "Rogue" in later editions), nimble combatant focused on stealth and social skills, also capable of high-damage special attacks balanced by sub-par resistance to injury
A common alternative to class-based systems, skill-based systems are designed to give the player a stronger sense of control over how their character develops. In such systems, players choose the direction of their characters as they play, usually by assigning points to certain skills (such as "hiding" or "forgery").
Character roles: Characters of a given class are said to fill a particular role in the party, especially in combat. Leaders are focused on buffing and healing allies. Controllers focus on affecting multiple targets at once, either damaging or debuffing them, or altering the battlefield's terrain. Defenders focus on blocking attacking enemies or drawing their attacks to themselves and are typically focused on melee combat. Strikers are focused on mobility, dealing heavy damage to single targets and avoiding attacks. While some Leader and Striker classes and builds are focused towards either melee or ranged combat, the roles as a whole are not.
- Tank (gaming), a common character class focused on drawing enemy damage.
- Healer (gaming) is another common archetype focused on restoring the health of one's allies.
- Spell-caster (gaming) is another common archetype focused on dealing damage, but is relatively weak in all other regards.
- DPS is another common archetype also focused on dealing damage.
[Healer (gaming) is another common archetype focused on restoring the health of one's allies. Spell-caster (gaming) is another common archetype focused on dealing damage, but is relatively weak in all other regards. DPS is another common archetype also focused on dealing damage.]
DPS - Damage Per Second