adsense vs adwords

[montyauto]

I have seen both adsense and adwords terminology being used from the same website.

I always thought they were the same, hope this only my thouth.

So which one between the both you prefer mostly and why?

[beu]

These two are opposites in terms of cost.

AdWords - ads paid for by advertisers. ($ out)
AdSense - ad space paid for by Google. ($ in)