Warmblood

Warmbloods are a group of middle-weight horse types and breeds primarily originating in Europe and registered with organizations that are characterized by open studbook policy, studbook selection, and the aim of breeding for equestrian sport. The term distinguishes these horses from both heavy draft horses ("cold bloods") and refined light saddle horses such as the Thoroughbred and Arabian ("hot bloods"). Although modern warmbloods are descended from heavier agricultural types systematically upgraded by hotblood influence, the term does not imply that warmbloods are direct crosses of "cold" and "hot".

Open studbook policies separate most warmbloods from true "breeds" such as Thoroughbreds, Arabians, Percherons, and Morgans which have a closed stud book and require two purebred parents. Instead, most warmblood registries accept breeding stock from other similar populations to continuously improve their own, and do not consider their own horses to be a discrete "breed". The Trakehner is an exception, as although some other breeds are used within the breeding population, this horse is considered a true breed. The Hanoverian, Holsteiner, and Selle Français studbooks are also considered slightly less open than others. Most warmblood registries recognize breeding stock from any other registry that is a member of the World Breeding Federation for Sport Horses which is affiliated with the IOC-recognized International Federation for Equestrian Sports.

A defining characteristic of a warmblood registry is studbook selection, though even some purebred breeds in Europe use this practice. Studbook selection is the use of external evaluation - critiquing conformation and movement - of potential breeding stock to cull unsuitable breeding horses and direct the evolution towards a particular goal. Today, studbook selection usually entails a performance proof in addition to external evaluation, particularly for stallions.

...
Wikipedia