Actually, backlinks and inlinks are just the same. Backlink or inlink is a link that can be obtained when another site links to your site. It is very important because the larger number of inlinks, the more your site will be noticed, visited, read and discussed.
Agreed, they are both the same. Sometimes when people say "incontent links" or "links in the content" - they mean a link inside a sentence/paragraph/article - rather than just a normal blogroll style link.
I just want to share this also, Search Engines Index Pages Not Sites. One of the biggest SEO mistakes one can make online is to optimize almost exclusively the homepage. This is done generally by building all the incoming links towards the homepage, what one fails to realize is that the search engines don't index "sites", they index "pages".