Sorceress

A sorceress is the female version of a sorcerer.

Alliance sorceresses
As with the elven priests, the elven sorceresses who remained in Lordaeron paid little heed to their race’s departure from the Alliance. These female magic users, serving as agents to the Kirin Tor of Dalaran, use their arcane powers to aid the Alliance in times of peril.

These female magi, sent by the Magocrats of Dalaran to watch over the volatile battle magi, use their arcane powers to aid the Alliance forces whenever Humanity is imperiled. Although their powers are not often used directly in combat, the sorceresses are able to aid the Alliance warriors with a wide array of specialized conjurings and magical effects.

Note that both high elf and blood elves sorceress have the symbol of Dalaran on their cloaks.

Though not often seen, humans can become sorceresses, too. Jaina Proudmoore is a sorceress and Antonidas speculated that she would become the finest sorceress humanity had ever produced.

High elven sorceresses
The Sorceress helped the high elves fend off Arthas as he tried to attack their capital Silvermoon City and Quel'Thalas in Warcraft III. It is a caster unit. It is produced at the high elf building called the high elf arcane sanctum. The blood elves also had sorceresses in The Frozen Throne expansion campaign in Warcraft III. Their damage and armor type are different than the expansion sorceress.

Clad in revealing robes, this elven sorcerer is distinctive. She wears far too much eye shadow.

Blood elf sorceresses
Sorceresses are a blood elf unit that is a caster. They appeared in the Warcraft III: The Frozen Throne human campaign to aid Kael'thas. It is produced at the Blood Elf Arcane Sanctum. They are completely identical to the High Elven counterpart with the exception of clothes, which have white parts replaced by red.

Trivia

 * In earlier screenshots and concept art Sorceresses were humans instead of high elves. Their description during the Warcraft III alpha was as such: "These female Magi, sent by the Magocrats of Dalaran to watch over the volatile Battle Magi, use their arcane powers to aid the Alliance forces whenever Humanity is imperiled. Although their powers are not often used directly in combat, the Sorceresses are able to aid the Alliance warriors with a wide array of specialized conjurings and magical effects."
 * Sorceresses in Warcraft III are known for being heavily sexualized, with revealing clothing and suggestive animations. Namely, during casting and death animations a Sorceress spreads her legs so her underwear is seen, and a rare portait animation has her levitate higher and display her cleavage to portrait camera, followed by teasingly showing her tongue. Probably as a decision to avoid controversy, in WoW, Sorceressess receive quite modest clothing: their robes now fully cover their bodies. However, revealing clothing similar to old Sorceress wear is still used by a few female characters, such as Sally Whitemane, Argent Confessor Paletress or Vanessa VanCleef.