Translations:EFI System Partition/59/en
From Gentoo Wiki
Most (U)EFI implementations support the use of the removable media boot path as a fallback on internal drives.[1] Even though this is against specification, most systems use it as a fallback and it may even be the only usable bootloader on a system with a buggy (U)EFI. Only one such fallback bootloader is possible on a specific system (i.e. architecture), due to the standardized boot path and file names.