"Why, thank you, Doctor."
Being cold-blooded was an informal term describing one who lacked the ability to maintain a constant body temperature. The opposite of cold-blooded creatures were often identified as warm-blooded creatures.
Xindi-Reptilian thermal chamber
Examples of living creatures that were cold-blooded included the reptilian Gorn and the Saurian Voth. (TOS: "Arena"; VOY: "Distant Origin")
Xindi-Reptilians were also cold-blooded, and even had a thermal chamber aboard their vessels to facilitate their physiological needs. (ENT: "The Council", "Countdown") After being captured by the Xindi, during Captain Jonathan Archer's interrogation aboard Reptilian Commander Dolim's warship, Archer was informed by Dolim the name of pilot, who operated the Xindi probe that attacked Florida, would "go down in history," and would be "spoken with reverence, a testament to the superiority of the cold-blooded." (ENT: "Azati Prime")
The last common ancestor to warm- and cold-blooded organisms on Earth
The Eryops, a creature that lived over four hundred million years ago was, according to The Doctor, "believed to be the last common ancestor of cold-blooded and warm-blooded organisms" on Earth. The most highly evolved cold-blooded organism to develop from the Eryops was the genus Hadrosaur, during Earth's Cretaceous Era. (VOY: "Distant Origin")
The reptohumanoid hatchling encountered by Neelix and Tom Paris in 2372, was described as being "cold-blooded, [and] has reptilian epidermis." They later observed that it was shivering, and after bundling in up for warmth, it stopped. (VOY: "Parturition")
Vulcans were often implied to be "cold-blooded", but the term was often more than not spoken idiomatically. Doctor Leonard McCoy often described Spock as being "cold-blooded"; even going to far to describe that "green ice water you call blood." (TOS: "Court Martial", "The Paradise Syndrome") Though having never met McCoy, Lara also shared the same sentiments, one sharing, "Vulcans. Never liked 'em much m'self. Cold blooded critters, all of 'em." (TAS: "The Jihad")