Let's say you have a beautiful garden with a well-manicured lawn, shimmering koi pond and brilliant bands of flowering plants. Now imagine some jerk shows up and starts dumping trash, ripping out flowers and pouring toxic waste into the water--it would take months to clean and would never look the same.
But if there was a way to contain the damage, say by building a small box around the perpetrator, cleanup would be a breeze and the rest of your garden would stay pristine.
Replace "jerk" with "malware" and "garden" with "Mac," and you've got the essence of sandboxing, a security measure that, in Apple's own words, "protects the system by limiting the kinds of things an application can do, such as accessing files on disk or resources over the network." So if, for example, your favorite music player suddenly decides it wants to randomly trash files on your system, the virtual sandbox will prevent it from doing that.
