The Schufa is a General Credit Protection Agency in Germany allowing companies to perform credit checks on their clients and individuals to seek information about their current credit status. The Schufa is a company that charges for every information issued. Every citizen and individual can obtain a free of charge statement of their current credit status once a year. For more information please see the official Schufa website.
More information on required documents:
Which documents do I have to submit for an apartment application?