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)

The Doctor
The Time Lords temporarily extracted the Second Doctor, followed by the First Doctor, from their respective time streams to assist the Third Doctor against Omega. The First Doctor, however, was caught in a time eddy and so could only provide his advice. (TV: The Three Doctors)

Lord President Borusa used Time Scoops to bring the first five incarnations of the Doctor, as well as several of their companions, to the Death Zone on Gallifrey as part of his plot to gain Rassilon's gift of immortality. However, the Fourth Doctor and Romana II were caught in a time eddy and so failed to arrive. After Rassilon granted Borusa the gift by confining him in the stone of the Tomb of Rassilon, the Doctors and their companions returned to their respective time and place. (TV: The Five Doctors)

The Tenth Doctor accidentally came into contact with the Fifth Doctor when their iterations of the TARDIS colided, resulting in the Fifth Doctor appearing in his successor's' TARDIS control room. This caused a paradox which risked the creation of a black hole that would endanger the universe. However, the Tenth Doctor was able to quickly enact a solution, having remembered watching himself doing so from the perspective of his predecessor. Bidding farewell, the Fifth Doctor returned to his own time soon after. (TV: Time Crash)

When the War Doctor prepared to use the Moment to end the Last Great Time War by destroying the Time Lords and the Daleks on Gallifrey, the sentient weapon brought him as well as the Eleventh Doctor from the Under-Gallery, into contact with the Tenth Doctor in Elizabethan England, where a Zygon incursion had been uncovered. After the three Doctors arranged a ceasefire between the Zygons and humanity in the 21st century, the War Doctor returned to the barn accompanied by his future selves, who had been let through the time lock. When Clara Oswald urged the Doctors to find another way to end the war, they got the idea to transport Gallifrey into a pocket universe on the last day of the Time War. To do so required the work of "all thirteen" of the Doctor's incarnations, up to the Twelfth Doctor. Following this, the Eleventh Doctor returned to the Under-Gallery where, after seeing off his predecessors, made contact with the Curator, an incarnation from his future. (TV: The Day of the Doctor)

The Thirteenth Doctor visited the Fourth Doctor whilst he was trapped in the pocket dimension controlled by the Scratchman, to give him a reminder of what he stood for and what he had to be in order to encourage him to hold on to his true identity against the Scratchman's power. Once her past self, Sarah and Harry were back on Earth, the Thirteenth Doctor visited the Fourth directly to muse on how important it was that they never give up on being the Doctor. (PROSE: Scratchman)

The Master
, the ninteenth incarnation of the Master, (PROSE: Girl Power!) inadvertently came into contact with her immediate predecessor aboard a Mondasian colony ship while in the company of the Twelfth Doctor. (TV: World Enough and Time) Though they initially joined forces, Missy ultimately elected to side with the Doctor against the Cybermen, resulting in her being killed without the opportunity to regenerate by her predecessor, though not before she mortally wounded him and thus initiated his regeneration. (TV: The Doctor Falls)

Others
Eleven of Drax's thirteen incarnations teamed up in order to con the Fourth Doctor into stealing a Blinovitch Limitation Effect limiter, which was what allowed them to cooperate on this scheme in the first place. (AUDIO: The Trouble with Drax)