Complex Space-Time Event

A CSTE, standing for Complex Space-Time Event (PROSE: Continuity Errors) or complicated space-time event (TV: Flesh and Stone) was an individual "of such blinding historical importance" that they "appeared bigger than whole worlds" on the Great Houses' charts of the Spiral Politic, a symbolic map of history which normally focused on the relationship between the interlocking timelines of whole planets. (PROSE: The Book of the War)

The term "CSTE" was coined by Professor Arthur Candy, who believed the Doctor to be "the most complex space-time event there has ever been anywhere". Highly skeptical of the Doctor's morality, Candy believed that as a CSTE, the Doctor warped reality around him without even needing to make explicit alterations via time travel, explaining how everything usually worked out for him even in extremely hostile environments. As such, "like all [CSTEs], he [could] not easily be studied because his very presence alters the way you think". (PROSE: Continuity Errors)

The Eleventh Doctor later described himself as a "complicated space-time event", noting that as such, throwing himself into a Crack in Time could "satiate" it for a while. River Song claimed to also be a complicated space-time event, but the Doctor claimed that she was nowhere near complicated enough for this purpose. A swarm of Weeping Angels taken together, on the other hand, just about "added up" to the equivalent of the Doctor's complexity. (TV: Flesh and Stone)

Jack Harkness, following his resurrection by the Bad Wolf, was identifed by the Tenth Doctor as an "impossible thing" and a "fixed point in time and space". (TV: Utopia, Last of the Time Lords) In one alternate timeline, Jack's death resulted in the end of the universe. (AUDIO: The Death of Captain Jack)