UEFI fdisk is a disk partitionning tool running under UEFI/BIOS
UEFI fdisk is a port to UEFI of the famous fdisk partitioning tool from util-linux, see https://github.com/karelzak/util-linux . Now since this program runs directly under UEFI shell you don't need to *boot* the system to edit partition tables.
UEFI GTP fdisk is a disk partitionning tool running under UEFI/BIOS
UEFI GPT fdisk is a port to UEFI of the famous GPT fdisk partitioning tool, see http://sourceforge.net/projects/gptfdisk/ . Now since this program runs directly under UEFI shell you don't need to *boot* the system to convert/edit partition tables.