A glass cockpit is a cockpit where flight data is shown on Electronic Flight Displays (EFDs) rather than separate gauges for each instrument. Examples of EFDs are the Primary Flight Display (PFD) which combines data from several instruments and is the pilot's primary source of flight information and the multi-function display (MFD) which allows data to be presented on multiple pages that are convenient to switch between. Another common name for these displays is Electronic Flight Instrument System (EFIS).
The use of electronic displays allows for better design solutions - the focus is shifted from trying to fit all necessary instruments into the small space of the cockpit to finding a way to present all importatnt information in a user-friendly way.