Err, Its the interaction level with the audience of your blog. That does not necessarily include the comments actually, in my personal opinion.
Interaction means how you narrate a story / post to your readers and the interaction level therein actaully. It means how impactful your post is from the perspective of the readers. How you engage them and how engrossed they would be.
Eg would be if you write a 2000 word blog post and judjes don't find (readers actually) readworthy after about 500 words, then your post is not interactive.
This is what I personally feel though.