An unreliable narrator cannot be trusted.
He comes in many guises. There is the delusional unreliable narrator, like Holden Caulfield in The Catcher in the Rye, unaware of how the reader and the other characters perceive him. There is the mad narrator, as in One Flew Over the Cuckoo’s Nest. There are the unreliable narrators who lie to themselves to make the unreality appear real. Middle-aged professor Humbert Humbert in Lolita famously lies to the jury and to himself, believing his sexual affair with the drastically under-aged Lolita is not criminal. Yet Vladimir Nabokov, the author, gives a wink to the reader: We know the protagonist is not being honest with himself.