It is a type of partition structure. GPT is a newer standard than MBR.
GPT (GUID Partition Table) takes advantage of BIOS UEFI to support storage devices larger than 2 TB and allows for easy configuration of as many partitions as needed (Microsoft Windows supports up to 128 partitions on a GPT disk). Windows 10 and Windows 8 or 8.1 can use UEFI BIOS, which can speed up startup and operation times and provides additional security benefits. To boot a computer in UEFI mode, you will need to use a drive formatted with the GPT drive format.