It's a software component that allows other software to work. Such as flash to make a game playable. If it gets lost, or more likely screwed up, it's normally because you've downloaded something else or removed a program or the evil computer genies have mad a mess of your stuff. Generally, you don't recover it in as much as you repair it or get another copy from a reputable site. Your computer will normally tell you what you need, then you'll have to search for and have to re-download it. Sometimes, if it is an adobe product or the like, it (the computer) will give you a notice and options of where and how to download it from the page giving you the message in the first place.