UEFI stands for 'Unified Extensible Firmware Interface'. It's a software system that starts up the computer when you turn it on, before Windows or your other operating system loads. UEFI helps the computer start faster and allows it to have more advanced features than older BIOS systems. Platform Initialization is a set of tasks that UEFI does when the computer starts up. Some of these tasks include checking the hardware, loading device drivers, setting up memory and starting the operating system. This helps make sure everything works properly and your computer starts up quickly and smoothly.