You're going to want to get a carrying case for your PSP to protect it from bumps and the elements, but what about the small stuff? The scratches and grit that could very well be inside of your carrying case, just waiting to love on your PSP's delicate young screen?
That's where Screen Protectors come in. These are thin plies of plastic that adhere to your PSP to take the abuse so your screen doesn't have to and then can be easily removed without any adhesive residue. They're disposable, so there's 4 of them in the pack.