This is an opportunity to provide some contextual information about the item you are uploading that isn't already included in the title.
For example:
If you intend uploading an oral history interview, you may wish to use this section to provide a brief overview of the topics discussed in the recording.
E.g. The interview centres around the events of the 1921 lockout. Topics discussed include soup kitchens, welfare halls and the support given to locked out miners and their families. In this 7 minute extract, the interviewee discusses the role of the welfare hall in arranging activities for locked out miners.
If you intend uploading a photograph, you may want to use this section to provide a description of the photograph (both content and format).
E.g. Black and white print measuring 10cmx8cm of Mumbles street scene. Shops line both sides of the street. In the foreground, two women are purchasing groceries from a greengrocer. A horse and cart can be seen in the background.