Authorial intrusion (noun): a literary device whereby the author speaks directly to the reader, establishing a connection between him or her and the audience and making him- or herself a subject of attention.
Example: It could be said that Jon Ronson’s confessions in The Psychopath Test are a type of authorial intrusion, but this device is more frequently used in novels than non-fiction. A more typical example is that of Kurt Vonnegut, who was famous for injecting his perspective into his stories. Here’s an example from Slaughterhouse Five that demonstrates exactly this:
An American near Billy wailed that he had excreted everything but his brains. Moments later he said, ‘There they go, there they go.’ He meant his brains. That was I. That was me. That was the author of this book.
(via Eat Your Words: Definition of Authorial Intrusion and Chiffonade)
