Standing taller than most Humans, Aurelians had six limbs: two arms, two legs, and two wings that allowed them to fly. They were covered by feathers that could be various colors including yellow, orange, brown, gray, and white. Their eyes typically had bright blue sclera, though Aurelians with white sclera also existed, with some possessing pupils and others lacking them. Aurelians typically did not wear clothing. (TAS: "Yesteryear"; LD: "Envoys", "An Embarrassment Of Dooplers")
The name Aurelian originated from the source's script. Specifically, the script of "Yesteryear" identified them by way Aleek-Om, which according to the stage directions, he was further described as "a native of the planet Aurelia, and he is a bird-like creature of blue-green hue." In the actual episode, he is instead a golden color. The novelization of "Yesteryear", appearing in Star Trek Log 1, describes the Aurelian Aleek-Om as having an "intricate scroll" – a sign of manhood – tattooed on his beak, "wide, black eyes," as well as a "brilliant gold and blue-green plumage."
The Aurelians closely resemble the Skorr, as Star Trek: The Animated Series reused the Aurelian character design for the Skorr as a budget-saving measure. (Star Trek Magazine issue 158, p. 52) In the text commentary to "Yesteryear", Aleek-Om is even described as a member of the Skorr. The Aurelian design differs from the Skorr in having a slimmer build, a thinner neck, and longer plumage on the hips. 
According to Brad Winters, Star Trek: Lower Decks uses a design closer to the original Skorr appearance for the Aurelians because it "looked cooler". He has suggested that the Aurelians and Skorr made peace and began to unify after discovering they were related, and thus some of the Aurelians seen on screen may actually be Skorr or Aurelian-Skorr hybrids.