Rayon is a synthetic material that feels a lot like silk.
It’s a fine material that is incredibly smooth, which is why it’s often marketed as “artificial silk” on labels.
It’s made from cellulose fiber (from plants), which means that rayon is almost always vegan.
The most common source used to extract rayon is wood pulp.
You might be able to find some weird unique form of rayon that for some reason used an animal product during the manufacturing process, but that would be very rare.