Movie Clip symbol?
When a Symbol is created, it defaults to 'Movie Clip'.
Is that a legacy from the Flash era?
As per the comment, it is still used in Animate.
Jan, it is still used in Animate. So when you import an artwork from Illustrator to Animate, it is imported correctly. If you are not using Animate (yes, it is former Flash), then there is no difference.
Monika covered this here: