Incarnation

The term incarnation was sometimes applied to the bodies/selves/lives of a Time Lord. While it was sometimes used interchangeably with "regeneration", (TV: The Keeper of Traken, Extremis) incarnations were actually the result of this process, with Time Lords regenerating from one incarnation to another.

Barring special circumstances, a Time Lord could only have thirteen incarnations, (TV: The Deadly Assassin) before their symbiotic nuclei started to break down. (AUDIO: Trial of the Valeyard) Some, like the Master (TV: Utopia, AUDIO: Eyes of the Master) and the Doctor, (TV: The Time of the Doctor) have been given new regeneration cycles, bypassing this limit.

Proto-Time Lords created by the Kovarian Chapter had varying numbers of incarnations. (AUDIO: The Lady in the Lake)

Contact between separate incarnations of the same Time Lord constituted a violation of the First Law of Time. (TV: The Three Doctors)

Use of the term
Looking back on their previous lives, the Doctor occasionally used the word incarnation. (TV: The Twin Dilemma, AUDIO: The Light at the End, The Chimes of Midnight, Dead London, Scaredy Cat) He also used it in reference to the Master, (TV: Doctor Who) and others used it to talk about the Doctor's regenerations, as well. (TV: The Ultimate Foe)

The Eleventh Doctor thought he had never used the word incarnation in that capacity but was proven wrong by Ally, from an alternate dimension, who played a clip from Doctor Who of the Sixth Doctor discussing his "last incarnation" in The Twin Dilemma. He conceded but claimed that the word was hardly ever used. (COMIC: The Girl Who Loved Doctor Who)

With the term being sometimes interchanged with the term regeneration, a Time Lord stating they were in their tenth regeneration would be synonymous in saying they were in their eleventh incarnation. (TV: Hell Bent)

When referring to past incarnations, the Doctor would use the plural "mes", faces or lives. (COMIC: Four Doctors) Time Lords might also use the term "bodies" or "body" when referring, generally, to either their own or other Time Lords' different incarnations. (COMIC: Doorway to Hell) On one occasion, the Sixth Doctor used the word "iteration". (AUDIO: The Light at the End)

Time Lords by incarnation
The number of the Doctor's incarnations was complicated; the Eighth Doctor's successor did not use the title of doctor, while the so-called Tenth Doctor once regenerated and kept his face. As such, the Eleventh Doctor had expended all his lives before being enabled to regenerate again by the Time Lords. (TV: The Time of the Doctor) Upon the "birth" of the Thirteenth Doctor, the Doctor had regenerated a total of fourteen times. (COMIC: The Many Lives of Doctor Who) A further incarnation was yet to come. (TV: The Day of the Doctor, COMIC: The Then and the Now)

In her Spacebook profile, identified herself as the ninteenth incarnation of the Master. (PROSE: Girl Power!) It was in this incarnation that she was killed by her predecessor, denying her the opportunity to regenerate. (TV: The Doctor Falls)

Drax was known to have had thirteen incarnations. (AUDIO: The Trouble with Drax)

In his thirteenth and final incarnation, Azmael deliberately regenerated past his limit, killing him and Mestor, who had been attempting to possess Azmael's body after his own was destroyed. (TV: The Twin Dilemma)

As her title suggested, the Twelve was the twelfth incarnation of a Renegade Time Lord who suffered from regenerative dissonance. (AUDIO: Planet of the Ogrons) Other than her, the Time Lord who lasted the longest with this condition shot out both his hearts with a staser in his eighth incarnation. (AUDIO: World of Damnation)

Kenossium was known to have had twelve incarnations. (TV: Hell Bent)