IBL => or inbound links = > Links from other websites pointing to your site.(Back links) OBL => outbound links => Links from your site pointing to other websites.
They basically refer to blogs that will earn your website greater benefit when you acquire links from them. Like the above responses, OBL stands for Outbound Links. And by saying low OBL, it usually means the count of outgoing links is less. To understand why you should consider posting your links on pages with low OBL, let's assume that you posted your link to two different pages. Both have PR 2; however the first page has 30 OBL while the second has 50 OBL. Now, to answer which of these pages give you more SEO value, let's compute the link juice you will earn from each of the pages with this formula PR / OBL = Link Juice per Link. Page 1: PR 2 / 30 OBL = 0.067 link juice to each OBL. Page 2: PR 2 / 50 OBL = 0.040 link juice to each OBL. The computation above assumes all OBLs are dofollow. As you can see, you will gain more SEO value from a page with low OBL than a page with a greater number of OBL.