An "Eeveelution" is any of the evolved forms of the Pokémon Eevee. Eevee, with its unstable genetic code, has the unique ability to evolve into one of eight different Pokémon, each with a unique type and abilities. These evolved forms are known as Eeveelutions.
Here's a more detailed look at the Eeveelutions:
Vaporeon: A Water-type Pokémon.
Jolteon: An Electric-type Pokémon.
Flareon: A Fire-type Pokémon.
Espeon: A Psychic-type Pokémon.
Umbreon: A Dark-type Pokémon.
Leafeon: A Grass-type Pokémon.
Glaceon: An Ice-type Pokémon.
Sylveon: A Fairy-type Pokémon.

Sylveon is a quadrupedal Pokémon with pale cream-colored fur, pink ears, feet, and tail, and light blue eyes. It has long, rabbit-like ears with dark blue insides, a short, blunt muzzle, and a small black nose. Sylveon is known for its soothing aura emitted by its ribbon-like feelers, which can erase hostility. These feelers, which can be manipulated like limbs, have pink and blue tips.
More Details:
Appearance:
Sylveon has white fur on its body, pink fur on its head, and pink ears with dark blue insides. It has a fluffy pink tail and slender legs with three-toed paws.
Behavior:
Sylveon is known for its gentle nature and can be seen using its feelers to hold hands with its Trainer. It is also known for its ability to sense feelings and use its feelers to soothe and calm others.
Habitat and Wild Behavior:
Wild Sylveon are often found in lush woodlands, where they can avoid hostility. They are known to be elusive but prefer the company of humans to other beings.
Evoletion:
Sylveon is an Eeveelution, meaning it evolves from Eevee.
Abilities:
Sylveon has the Cute Charm ability, which can cause an opponent to feel affection for it, according to Pokemon Wiki.
Other Notes:
Sylveon's name comes from the words "sylvan" (of the forest) and "eon," possibly referring to fairies or mythological spirits. Its Japanese name is "Nymphia," which is based on the word "nymph"