Kitab kuning , "yellow books," is the name by which the Arabic textbooks and works of reference studied in Indonesian pesantren , Islamic religious boarding schools, are commonly known. Occasionally, the Arabic equivalent, al-kutub al-ṣufrā , is also used. The origin of the term is not entirely clear, but it probably refers to the colour and quality of the paper of cheap Egyptian mass-produced prints. By extension, the term also refers to the entire curriculum and the didactic methods of the traditional pesantren , especially as contrasted with that of reformist