Sometimes, you will see CD or DVD bundles for old Macs that come with both a "Software Restore" and a "Software Install" disk.  What's the difference?

The software RESTORE disk will wipe the whole hard drive and reinstall everything (OS, utility apps, game demos, documentation, etc) to the factory condition.  This will leave it completely free of any previous DATA.

The software INSTALL disk will let you individually choose what to install or re-install so you can, for example, only re-install an app that has been deleted by mistake or you could even just install the whole OS on the side of the previous one, so without deleting your settings and personal files.