As used in NRS 389.840 to 389.880, inclusive, unless the context requires otherwise:

1.  ’Basic textbook’ or ‘textbook’ means any medium or manual of instruction, including, without limitation, software for computers, containing a presentation of the principles of a subject and used as a basis of instruction.

2.  ’Supplemental textbook’ means any medium or material, including, without limitation, software for computers, used to reinforce or extend a basic program of instruction.

3.  A basic or supplemental textbook becomes ‘unserviceable’ when 4 years have elapsed since its removal from the adopted list.