"Whenever we encounter a first person narrator in a novel, we as readers know we're getting a character's version of the story rather than directly witnessing the events as they actually happened. S0 in a way, one could argue that every first-person narrator is an unreliable narrator, but some narrators are more trustworthy than others. A narrator is "unreliable" when we have reasons to doubt the versions of events he or she is presenting to us as factual in a story. Whether it be for reasons of mental instability or self-preservation, we know the narrator isn't disclosing everything to us, or isn't telling us the whole truth."
NOTE: There was actually 51 books in the Book Riot's list