A flaw, fault, or indiscretion within oneself, especially compared to a lesser fault one is criticizing in someone else (often worded as a "mote" in their eye). A reference to two passages in the Bible (Luke 6:42 and Matthew 7:5), both of which state that one should not criticize the faults of someone else before correcting the faults within oneself. It's pretty unfair of you to get mad at her for talking with other guys in a flirtatious way, when you've admitted to cheating on her before. You should inspect the beam in your eye before getting mad about the mote in hers.