Incarnation

An incarnation was the term 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 and the Doctor, have been given new regeneration cycles, bypassing this limit. (TV: The Keeper of Traken, The Time of the Doctor)

Contact between seperate 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 his 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) 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)

The Doctor
It is difficult to establish how many incarnations the Doctor has had. The Doctor, whilst fighting during the Time War, did not refer to himself as "the Doctor", and after apparently committing genocide, his future selves disown this incarnation (the ninth of thirteen). The so called Tenth Doctor (his eleventh incarnation) wasted one regeneration and created a half human/Time Lord. Therefore the Eleventh Doctor has by this point no more regenerations. On the verge of dying of old age at the Siege of Trenzalore, the Doctor was granted a second regeneration cycle by the Time Lords through a crack in time above the planet, allowing him to resolve the conflict and regenerate for the thirteenth time. (TV: The Time of the Doctor)

The Master
With all twelve of his regenerations expended, the thirteenth incarnation of possessed the body of the Trakenite Tremas. (TV: The Keeper of Traken) Later, the Master escaped his execution at the hands of the Daleks by assuming the form of a deathworm morphant, with which he possessed the body of a human named Bruce. (TV: Doctor Who) After ultimately dying, the Master was resurrected by the Time Lords, with the process enabling him to regenerate again. (TV: The Sound of Drums) The incarnation of the Master who called herself recalled that she had "died" eighteen times prior, making her the Master's ninteenth incarnation. (PROSE: Girl Power!)