Fraternal twins, scientifically known as "Dizygotic Twins", are twins who share 50% of their DNA, being no different, genetically, than normal siblings.
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Fraternal twins are the result of two separate egg cells being fertilized by two separate sperm cells, after which both successfully implant in the same womb during the same pregnancy.
Both siblings share only 50% of their DNA as a result. This means these siblings can develop to be wildly different, having differing secondary sexual characteristics or hair, eye, and fur colors, and are, aside from their births being minutes apart instead of years, otherwise no different than any other pair of siblings.

Fertilization of the two eggs can occur either simultaneously, and can even occur days later if a mucous plug had not yet formed in the cervix. During development, both embryos have their own placenta and amniotic sac, however, the absence of multiple placentas or amniotic sacs in artwork does not inherently preclude this tag from use

Fraternal twins are visually indistinguishable from normal siblings. To follow TWYS, this should not be tagged without evidence in the image.

See also

• twins (lore): Tag for characters that are twins, regardless of how much DNA they share.
• half-identical twins: Tag for characters that share 75% of their DNA.
• identical twins: Tag for characters that share 100% of their DNA.
• Superfecundation on Wikipedia: Information about how twin eggs can be fertilized at separate times.
• Dizygotic (fraternal) twins on Wikipedia: Information about Dizygotic Twins.