The document discusses International Standard Serial Numbers (ISSN). It defines serials as publications issued in parts bearing issue numbers or dates that are expected to continue indefinitely, such as magazines, journals, and newspapers. The ISSN was developed as a standard numeric code to uniquely identify serial titles, making tracking and citing them more efficient. The ISSN is an 8-digit number, with a check digit as the 8th digit to detect errors. ISSN registration and coordination occurs through a international network, with national registration initiating where serials are published. The ISSN simplifies processes like ordering, checking in, interlibrary loans, and copyright payments for serials.