This is a process in which we hide the main links and redirect them to some other link. With this the main links are hidden and other links are shown. I mean to cloak the links / URLs of any affiliate program according to your own.
Google does not like many affiliate links and because of these Google can penalize our site. It is used to protect your blog from google penalty.
Also, it is better for the readers as well. They do not know whether this is a commission link or a link to your site itself. This process is also called Mask Affiliate Links. That is, wearing a mask to the link.