“Install boot” is an informal, ambiguous phrase, but it almost always points to a critical low-level task: making a computer start properly. Whether you are writing a bootloader to disk or booting a USB stick to run an installer, understanding the separation between booting and installing will save you hours of confusion.
bootrec /rebuildbcd : Scans all disks for installations and lets you add them back to the boot menu. 5. UEFI vs. Legacy BIOS: Why it Matters
Learning how to configurations manually gives you total control over your hardware. While the process varies between Windows and Linux, the logic remains the same: you are providing the "map" your computer needs to find its soul (the OS).
The second (and more literal) meaning is the act of to install a new operating system.