It means you erase the drive then reinstall the operating system. More precisely for Tiger it's called Erase and Install. It's an option of the OS X installer. The following is how it's done in Leopard, but the process is identical in Tiger.
To install Leopard using an Erase and Install do the following:
1. Insert the Leopard DVD into the optical drive and restart the computer.
2. After the chime press and hold down the "C" key until the spinning gear appears below the dark gray Apple logo.
3. After the installer loads select your language and click on the Continue button.
4. After the menu bar appears select Disk Utility from the Utilities menu.
5. After DU loads select your hard drive (this is the entry with the mfgr.'s ID and size) from the left side list. Note the SMART status of the drive in DU's status area. If it does not say "Verified" then the drive is failing or has failed and will need replacing. SMART info will not be reported on external drives. Otherwise, click on the Partition tab in the DU main window.
6. Click on the Options button, set the partition scheme to GUID for an Intel Mac or APM for a PPC Mac then click on the OK button. Set the number of partitions from the dropdown menu to one (1). Set the format type to Mac OS Extended (Journaled.) Click on the Partition button and wait until the volume mount on the Desktop.
7. Select the volume you just created (this is the sub-entry under the drive entry) from the left side list. Click on the Erase tab in the DU main window.
8. Set the format type to Mac OS Extended (Journaled.) Click on the Options button, check the button for Zero Data and click on OK to return to the Erase window.
9. Click on the Erase button. The format process can take up to several hours depending upon the drive size.
Steps 7-9 are optional but should be used on a drive that has never been formatted before, if the format type is not Mac OS Extended, if the partition scheme has been changed, or if a different operating system (not OS X) has been installed on the drive.