Elwin "Leper "Lepellier is the first boy in Gene and Finny's class to enlist in the war in A Separate Peace by John Knowles. Leper has always been rather odd, and the circumstances of his enlistment are not unsurprisingly odd. Once he is gone, the boys back at Devon School make up all kinds of adventurous feats they imagine Leper is doing, but they learn the worst has happened when he sends a letter to Gene which says that he has gone AWOL (absent without leave). It is one of the worst offenses a soldier could be accused of while in the Army; however, there is at least one thing worse than that.
Gene goes to visit Leper as requested and finds Leper to be different than he was. He is both more odd and more fearful; he is also clearly angry. He tries to tell Gene how things were for him when he was in the Army, but Gene cannot understand--and frankly does not try very hard to do so. It becomes clear that Leper was suffering some kind of mental breakdown during his short time in the service.
Leper explains that he left the Army because the only alternative would have been a Section Eight discharge. He explains that a Section Eight discharge is
"for the nuts in the service, the psychos, the Funny Farm candidates."
A Section Eight is the worst kind of discharge--even worse than a dishonorable discharge--because this label stays with soldiers for the rest of their lives. He will not be able to get a job and will be seen as some kind of freak by anyone who discovers the Section Eight designation in his past. He adds:
"you're screwed for life, that's what a Section Eight discharge means."
Leper is mentally unstable enough, it seems, to warrant a Section Eight discharge; however, he is obviously clear-minded and sane enough to know both that he qualifies for this designation and that, if he gets it, his life will be ruined.