The term warm-blooded is a colloquial term to describe animal species which have a relatively higher blood temperature, and maintain thermal homeostasis primarily through internal metabolic processes. These are characteristics of mammals and birds.

Both the terms "warm-blooded" and "cold-blooded" have fallen out of favour with scientists because of the vagueness of the terms and an increased understanding of the field. Body temperature types are not discrete categories. Each term may be replaced with one or more variants (see the next section for examples). Body temperature maintenance (thermoregulation) incorporates a wide range of different techniques that result in a body temperature continuum.

Warm-bloodedness generally refers to three separate aspects of thermoregulation.

A large proportion of the creatures traditionally called "warm-blooded", such as mammals and birds, fit all three of these categories. However, over the past 30 years, studies in the field of animal thermophysiology have revealed many species belonging to these two groups that do not fit all these criteria. For example, many bats and small birds are poikilothermic and bradymetabolic when they sleep for the night, or day, as the case may be. For these creatures, the term heterothermy was coined.

Freeman John Dyson FRS (born December 15, 1923) is a British-born American theoretical physicist and mathematician, famous for his work in quantum electrodynamics, solid-state physics, astronomy and nuclear engineering. Dyson is a member of the Board of Sponsors of the Bulletin of the Atomic Scientists. Dyson has lived in Princeton, New Jersey, for over fifty years.

Dyson's father was the English composer Sir George Dyson; his mother was trained as a lawyer but after Dyson was born worked as a social worker. Despite sharing a last name, he is not related to the early 20th century astronomer Frank Watson Dyson, but as a small boy Freeman Dyson was aware of Frank Watson Dyson. Freeman credits the popularity of an astronomer with the same last name as having inadvertently helped to spark his interest in science.^{[citation needed]}

Dyson has six children, two of them (Esther and George) with his first wife, mathematician Verena Huber-Dyson, and the other four with his second wife, Imme Dyson, a masters runner who married him in 1958. Due to issues with some of his children not being recognized as British citizens he abjured his allegiance to Britain, and became a naturalized American citizen.