It simply means Unified Extensible Firmware Interface.
All computers and laptops powered with windows 8 have the UEFI mode. Their start key has a windows 8 logo rather than the previous logo of windows company.
This mode helps you secure boot windows 8. When booting your computer, its company logo should appear when UEFI is enabled. You cannot install any OS(including earlier versions of windows) apart from windows 8 and later versions. To enable/disable this mode, you should access your computer's setup configuration during startup before the computer boots.
