The HD Loader is an application (.ELF) for your PS2 that you can run off your memory Card, an USB Stick or a CD an then load your games off the Hard Drive that you can connect over the Network Adapter with you Fat PS2.
I slipped and fell on ice in the parking lot at my apartment complex a little while back, managed to fall onto my knee and catch myself in a pose like a Spartan doing armor lock in Halo Reach lmao