Earth Reptile

Earth Reptile was a title used by Silurians to refer to themselves, ignoring other terms such as "Silurian", "Eocene", and "Homo Reptilia". They referred to their Sea Devil cousins, considered a sub-species, as "Sea Devil Warriors," possibly excluding them from the title. (PROSE: The Scales of Injustice)

Historians who had been allowed access to the "Monster Vaults" of the databanks in the Doctor's TARDIS observed that the Silurians and the Sea Devils were named as such by unfamiliar humans while also using the names for themselves, their explanation being that it was the proper name for the species which humans retained as ancient race memories. (PROSE: The Monster Vault)

During the time of the Earth Empire, it was a broad term for the Silurians, Sea Devils and related species, now accepted by humanity because of their Earth-born ancestry. It was considered to be more politically correct to refer to them as such, (PROSE: Love and War) though some thought the term was offensive and the sign of an assimilationist. (PROSE: Burning Heart) The term, however, continued into the time of the Union. (PROSE: The Crystal Bucephalus)

Speculating on the meaning of "Rep", the Eighth Doctor joked the enemy could be "eighty-seventh-century Earth Reptiles with transforming T.rex time machines" and that the entirety of human history could be a Time Lord attempt at eradicating their causal nexus. (PROSE: The Taking of Planet 5)