Adsense For Youtube is one of google adsense service that link to youtube. It is similar to google adsense, but this is only applied to video that uploaded to youtube. Adsense is belong to show ads on a site online, so adsense for youtube is belong to show adsense ads on videos. The publisher will be paid because of ads showing on his videos of clips on youtube channel.
The different between regular google adsense is that anyone which have account adsense for youtube, he cannot apply the ads on his website, so just only on youtube. While the regular one (someone that have non hosted google adsense account), he can apply google ads everywhere (on blog, website, forum, youtube) that not violate to google term of services (TOS).