Skin lightening is a process in which you use special treatments, mostly targeted creams, that literally turn darkened areas of your skin (dark spots, age spots, melasma, etc) lighter to get rid of them. This method of getting rid of dark spots and other hyperpigmentation hasn't been around very long but it's definitely becoming more and more accepted because of how well it works.
Sure, there are products available for as cheap as $10 but when it comes to skin lightening cream the phrase "you get what you pay for" holds very true. $10 creams don't do squat. Meladerm, priced at a moderate $49 is great, though. There are creams that cost as much as $110 that don't perform as well as Meladerm does.
NOTE: Unfortunately the Kardashian product is no longer recommended. It was a decent product when it was first released but they have since changed the formula and it is now ineffective and can cause breakouts.