Gallifreyan

Gallifreyans were a humanoid species native to the planet Gallifrey. The majority of Time Lords were Gallifreyans, since they arose from this species, and they considered themselves to be the elite of Gallifreyan society. (PROSE: Interference - Book Two)

Appearance and biology
Gallifreyans were externally identical in appearance to humans but had several biological differences internally. They had two hearts, (TV: Spearhead from Space) two or three brain stems, (TV: Spearhead from Space, The Magician's Apprentice) and a respiratory bypass system. (PROSE: Island of Death, et al.) Compared to humans, they also boasted larger brains, (TV: The Brain of Morbius) and lower body temperature. (AUDIO: Blood of the Daleks)

Culture and society
There was always a Lord or Lady President of Gallifrey, with a council of other Time Lords, approving or vetoing decisions. An exception to this was when the Lord President (ignoring the Chancellor) broke two Laws of Time to bring the First, Second and Third Doctor together to solve the problem of the power/life force-drainage into Omega's black hole. (TV: The Three Doctors)

Time Lords and Gallifreyans regarded the Flower of Remembrance as an omen of death. (PROSE: The Ancestor Cell)

A quarter of Gallifreyans on their homeworld worshipped the higher Eternals such as Death and Time. (PROSE: Happy Endings)

Gallifreyans and Time Lords
Sources differed on the difference (if there was any) between Gallifreyans and Time Lords.

Time Lords may have been just Gallifreyans in possession of a TARDIS. (AUDIO: Omega)

I.M. Foreman stated that Time Lords were a separate species due to Rassilon's intervention. (PROSE: Interference - Book One) The Eleventh Doctor and Vastra said that the Gallifreyans evolved into Time Lords via exposure to the Time Vortex and the Untempered Schism over billions of years. (TV: A Good Man Goes to War)

There was a community of Gallifreyan, non-Time-Lord farmers in the Drylands. (TV: Hell Bent) The Doctor spent some time among them in his first incarnation, sleeping in a barn as a young boy. One night, a man was overheard saying that the Doctor would have to join the army when he grew up, believing he lacked the potential to be a Time Lord. (TV: Listen)

At one point in Gallifreyan history, members of Gallifreyan religious orders who were not Time Lords were nonetheless given certain rights: access to time travel, certain genetic privileges, and the right to observe High Council procedure. However, the High Council later disestablished the churches, monasteries and other religious orders, effectively abolishing these rights. (PROSE: Interference)

Despite the fact that the vast majority of Time Lords were Gallifreyans, many Time Lords were non-Gallifreyan. (PROSE: The Infinity Doctors) These included Ace, (AUDIO: Intervention Earth) members of House Paradox, (PROSE: The Book of the War) Lolita, (AUDIO: The Shadow Play) and River Song. (TV: A Good Man Goes to War)

Within the Capitol
Even within the Time Lord sanctum of the Capitol, "plebeian classes" existed. (TV: The Deadly Assassin)

Outsiders and outcasts
Billions of Gallifreyans lived outside the Capitol and the other cities of the Time Lords. They made up almost the entire population of Gallifrey. They lived on farms or homesteads and worked through the day to provide food for themselves and the Time Lords in the cities. (PROSE: A Brief History of Time Lords)

Bands of Gallifreyans called the Outsiders dropped out of the Time Lord Academy and lived in the Drylands to reconnect with nature. They lived a primitive lifestyle, wearing fur skins and using weapons like bows, arrows and spears for hunting food. (TV: The Invasion of Time, PROSE: A Brief History of Time Lords)

Within the Capitol, rebels known as Shobogans committed petty acts of vandalism. (TV: The Deadly Assassin)

Gallifreyan Gallifreyanos