User blog comment:MsD/BOARDSCRAFT 1.6.2 BLOG/@comment-18933973-20130718141441/@comment-4599112-20130718170219

Ultra-HardCore(UHC) is a gamemode invented by the folks from the Mindcrack Server(A private vanilla server, accessed by invitation only) where natural health regeneration is turned off. (meaning that even if you have a full hunger bar, your health won't regenerate)

The only way to regain health is by eating golden apples and drinking health and regen potions.