Dropout

noun

1. Someone who has left an educational institution without completing the course

   "The politicians of the world are mere political university dropouts."

2. Someone who has opted out of conventional society.
3. One who suddenly leaves anything, or the act of doing so.
4. The slot in the frame that accepts the axles of the wheels.
5. A damaged portion of a tape or disk, causing a brief omission of audio, video, or data.