What do you mean by "short introduction"?
A short introduction should be a very short description of your submission.
This is equivalent to the size of a tweet (280 characters) which defines your submission and allows organisations and judges to have an immediate understanding of what they are looking at. Short descriptions are especially important when organisations are managing hundreds of applications. They may also be used for social media
This may feel like repeated information from the works description, but descriptions are not capped, and give you more space to define your work.