"Newblood" was an informal term for Time Lords of newer Houses. Newblood Time Lords were Loomed with a secondary heart (PROSE: Christmas on a Rational Planet) and had better rebirth-control than older Houses; (PROSE: The Book of the War) for this reason, they viewed regeneration as trivial and never played Eighth Man Bound at the Time Lord Academy. (PROSE: Christmas on a Rational Planet)
Newblood Houses were more likely to produce interventionists, and some even viewed time-active cultures as not being lesser species; for these reasons, they were often viewed by Oldbloods as smug and ambitious upstarts. Despite its long lineage, after it produced the Imperator, House Dvora was one of the first Newblood Houses, but it was far more stable than the eccentric Newbloods that would spring up during the War in Heaven. (PROSE: The Book of the War)
At the auction for the Relic, the Shift wondered if the Eighth Doctor was representing one of the newblood Houses. (PROSE: Alien Bodies)