Deep linking refers to “the practice of linking to the inner pages of another web site - as opposed to linking to the homepage” (Search Engine Dictionary). From a search optimization standpoint, deep links are a very desirable type of inbound links as they are allegedly given high value in the search algorithms. This thinking seems sensible for a few reasons. First, it is logical to assume that sites with deep inbound links have good content that other website owners want to link to. Second, deep links seem more natural than links to root of the web site, because deep links usually point to a related resource.
The problem with deep inbound links is that they are very difficult to obtain. Getting directories to link to a page within the web site instead of the main page is very difficult. The few deep links that exist in directories are usually pointing to great and unique resources.