Link units display a list of topics that are relevant to the content of your page.
Link units are closely targeted to the interests of your users. Because users directly interact with the ad unit, they may be more interested in the ads they eventually see.
AdSense publishers are paid for clicks on the ads that are linked from link unit topics, not for clicks on the initial topics themselves. The ads on the linked page are pay-per-click Google ads similar to those shown in regular AdSense ad units.
Responsive link units allow you to support a wide range of devices (i.e., computers, phones, tablets, etc.) by automatically adapting their size to fit your page layout. They're intended to work with sites built with responsive design, but will work on non-responsive sites too. Regardless of which device users use to visit your site, responsive link units can help you provide a great ad experience.