Wiktionary
alt. (context computing English) A computer disk holding a bootstrap loader and an operating system. n. (context computing English) A computer disk holding a bootstrap loader and an operating system.
Wikipedia
A boot disk is a removable digital data storage medium from which a computer can load and run ( boot) an operating system or utility program. The computer must have a built-in program which will load and execute a program from a boot disk meeting certain standards.
While almost all modern computers can boot from a hard drive containing the operating system and other software, they would not normally be called boot disks. CD-ROMs are the most common forms of media used, but other media, such as magnetic or paper tape drives, zip drives, and more recently USB flash drives can be used. The computer's BIOS must support booting from the device in question.
Usage examples of "boot disk".
He named the program Detective then compiled and copied it to the boot disk Sanchez had given him.
The first time I successfully installed Linux, I finally hit on something that worked by using the boot disk from one distribution with the CD-ROM for another.