This is also completely different from a clean install of OS X, which is performed by erasing a Mac drive and then starting fresh with a new clean installation of the Mac OS X system software.
The premise is mostly the same booting into Recovery mode to reinstall the system software. Newer MacOS releases also support the ability to re-install only macOS while leaving user files alone, however. If performed correctly as described, applications and user data will be preserved and not be modified at all, since this approach only reinstalls the operating system and system files. In these circumstances, sometimes the only solution to get things working again is to reinstall OS X system software or, if you have a recent safe backup made, restoring from Time Machine is often valid as well.
