What really do people mean by a supplementary disk ?

[<shyamk eth net>]

I read a specification for a Networking practice (Linux) ,
mentioning as requirements :
1. boot floppy
2. Installation CDs for Linux 6.0 
3. Supplementary disks .

What does 'supplementary disk' really mean ?
What can its contents be ?
How do you make it ?

Is theis the old Unix - root floppy thing ?

Thanks in adv.
(shyamk@eth.net)
Shyam