Translations:EFI System Partition/72/en
From Gentoo Wiki
Note
To boot from removable media, the firmware has to look for compatible bootloaders on supported devices, which can be configured in the firmware setup. Like most firmwares, (U)EFI provides a hotkey to show a boot selection (formally known as "BIOS Boot Specification" or BBS), otherwise (U)EFI will use the configured default boot entry. However, a buggy (U)EFI may default to the removable media boot path even on internal drives.
To boot from removable media, the firmware has to look for compatible bootloaders on supported devices, which can be configured in the firmware setup. Like most firmwares, (U)EFI provides a hotkey to show a boot selection (formally known as "BIOS Boot Specification" or BBS), otherwise (U)EFI will use the configured default boot entry. However, a buggy (U)EFI may default to the removable media boot path even on internal drives.