This article explains the UEFI boot mode on Elo all in one devices

UEFI boot mode refers to the boot process used by UEFI firmware and not the BIOS firmware.

UEFI (Unified Extensible Firmware Interface) stores information about initialization and startup in an .efi file that resides on the EFI System Partition. 

During the POST (Power On Self Test) procedure, the UEFI firmware scans the bootable storage devices that are connected to the system for a valid GUID Partition Table.

The firmware scans the GUID Partition Tables to find an EFI Service Partition from which to boot. If the EFI bootable partition is not found, the firmware may revert to the Legacy Boot process. If both UEFI boot and Legacy boot are unsuccessful, you may see a disk boot failure error message.