An inner or interior part. Inward character, perceptions, or feelings: felt good on the inside about volunteering to help. An inner side or surface. The part away from the edge; the middle part. Informal The inner organs; entrails. Informal The inner parts or workings: the insides of a TV set. Slang Confidential or secret information. Inner; interior. Relating to, known to, or coming from an exclusive group: inside information; an inside joke. Baseball Passing on the side of home plate nearer the batter. Used of a pitch. Into or in the interior; within. On the inner side. Slang In prison. Within: We'll be there inside an hour. On the inner side or part of: inside the package. Into the interior of: going inside the house. inside out With the inner surface turned out; reversed: wore the sweatshirt inside out. inside out Informal As completely as possible; thoroughly: knew the city inside out. on the inside In a position of confidence or influence.