A Time Lord is not a race of beings. Rather, it is a title awarded when a Gallifreyan completes his or her years at the Academy. Gallifreyans are an unusually humanoid race from the Doctor Who continuum. They have, or had, a highly advanced civilization which manipulated time and space readily; TARDISes were invented and used by them. Female Time Lords are sometimes referred to as Time Ladies.
Time Lords themselves are able to live to advanced ages, several hundred years; additionally, when they die, either of natural causes or from violence or illness, they are able to regenerate into a new body, with all the memories of the old one but a new personality. Time Lords can regenerate up to twelve times before they finally die; there are a few exceptions to this rule, such as extermination by a Dalek (unless Uncle Rusty's at the helm) or specific Time Lord technology, in which case they die for good. With the destruction of Gallifrey, their home planet, the current surviving Time Lords may have more possible regenerations.
The Doctor is perhaps the best known Time Lord, and is currently in his eleventh regeneration. While in his eighth regeneration, he took part in the Last Great Time War during which Gallifrey, home of the Time Lords, was destroyed, along with most of the Time Lords themselves. It is implied that The Doctor himself destroyed Gallifrey. Despite this, both the Doctor and the Master survived.
The standard Time Lord disguise includes a complete regeneration cycle, a fact some Agents have exploited to cheat death.
Additionally, multiple Time Lords are known to have survived by being in the PPC at the time. These are: