Media is a collection of files that belong to a project. These files can be anything that you can typically save on a regular computer desktop. This includes images, videos, Word documents, PDF's, SVG's, Excel spreadsheets, CSV files, JSON files, zip files, and anything else that you can think of.
Media can then be attached to individual records. This is powerful because it allows easy integration with content. If you have a Model of a Car and a collection of Cars - you would want every car to have it's own picture, or video review, this can be attached to each record and available through the API.
Fuchsia provides an API along with the user interface to upload, edit and remove assets from your media library. To have the records API return assets fully loaded, use the query paramter
loadAssets=true when requesting records that will include Assets.