Raw data is what we call the white and dark likes that comes from the process called electrophoresis. The dark lines are called bands. A dark band means that a reaction has happened. This means that the base is single. If the base had been paired to another base, it would have been protected, so it would not have reacted.
Teaching about Raw data
Pablo gave a fine explanation on how to read the raw data, under his presentation at the first monthly live developers meeting.