This excerpt taken from the VRSN 10-K filed Jul 12, 2007.
Schedule of Reserved Names
Except to the extent that ICANN otherwise expressly authorizes in writing, the Registry Operator shall reserve names formed with the following labels from initial (i.e. other than renewal) registration within the TLD:
A. Labels Reserved at All Levels. The following names shall be reserved at the second level and at all other levels within the TLD at which Registry Operator makes registrations:
B. Additional Second-Level Reservations. In addition, the following names shall be reserved at the second level:
C. Tagged Domain Names. All labels with hyphens in the third and fourth character positions (e.g., bq1k2n4h4b or xnndk061n)
D. Second-Level Reservations for Registry Operations. The following names are reserved for use in connection with the operation of the registry for the Registry TLD. They may be used by Registry Operator, but upon conclusion of Registry Operators designation as operator of the registry for the Registry TLD they shall be transferred as specified by ICANN: