"Degenerate" is one of the Negative Traits that a Crew members can have. It has the effect that when players Visit a Port, any Crew member they have with the Degenerate Trait must be placed on the DRINK or GAMBLE space. After triggering that action, the Degenerate Crew member may be moved to another Port space.
Sometimes, a card effect can say that a specific Crew member gains Degenerate; that means you should discard any previous Negative Trait card the Crew member might have, then search the Negative Trait deck for a Degenerate card and give that to the Crew member.