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 in case the configured EFI boot entries are not working (i.a. a fallback), e.g. in case the boot entries are defunct (like missing files), or the EFI variables (accessible on Linux using efivarfs) are lost, e.g. failure of the persistent store (like when the NVRAM is reset, cleared or becomes corrupted, which may occur when the "CMOS battery" fails). With a buggy (U)EFI it may even be the only usable bootloader on that system. Only one such fallback bootloader is possible on a specific system (i.e. architecture), due to the standardized boot path and file names.