A PSP - Sony PlayStation Portable - screen is clear and large. This widescreen image is almost a magnet for fingerprints, dust and scratches. This filter by Hori helps to protect this screen from damage.
In essence it's a clear plastic layer that you place down with a sticky substance on your PSP screen. You need to clean your screen VERY well to start with. We have eyeglass cleaner in the house and it worked perfectly - not a speck of dust or lint was left when we began.
Then we carefully followed their instructions to lay down the screen. It went down without any problem at all, and was crystal clear once it was down. Playing through it did not present any issue, and it really does a good job of keeping oils and dust away from the actual screen surface.
Since you only have one screen for your PSP, which you can't replace, it really is important to keep it clean. If that screen gets scratched, it affects the gameplay of everything you do from that point forward.
Buy PSP Screen Filter from Amazon.com