What does "Water/Flood" damage actually mean, and is it a dealbreaker for repair?

It means the vehicle was submerged or otherwise exposed to significant water intrusion, which can affect the engine, electrical systems, upholstery, and corrosion-prone components depending on depth and duration. It isn't automatically unrepairable — light flood exposure is sometimes fixed economically — but electrical and corrosion issues can surface months later, which is why flood vehicles carry a higher risk profile and tend to need a thorough mechanical and electrical inspection before any repair investment.