Affiliate directories are place where you can add your site for affiliate programs. It is important for starting affiliate marketing.
It's pretty much exactly like it sounds. It's a directory of affiliate programs. Its a good one to find an affiliate program that works well with your niche or website.
If you are looking to recruit affiliates then advertising your affiliate program in a Affiliate Directory will be one of the smartest things you can do. Also you can add your website to something like clickbank for $49.00. Now your website can be seen by hundreds of affiliates.