The Chimera or Chimaera (pronounced keye-MIR-uh, plural Chimerae) was "a fire-breathing she-monster in Greek mythology having a lion's head, a goat's body, and a serpent's tail." The monster was slain by Bellerophon, riding the winged horse, Pegasus.
The term has multiple uses in modern biology. One prominent definition is an animal that has multiple different populations of genetically distinct cells that originated from different zygotes. Some humans are naturally chimeric, sharing cells from a twin (often one that was never born) or a parent.
In popular usage, a chimera means something deliberately created with a combination of human and animal cells. Such combination is often opposed on religious and ethical grounds. Some Catholic bishops have argued that such embryos should not be created but should be brought to term if created in contrast to proposed legislation in Great Britain which would allow both the creation of chimeras and outlaw the implantation of a chimera once created.