Hola. One of New Shorter Oxford's entries for "slack" is: "b. Esp. of heat or the wind: not strong, gentle, moderate" and "reduce the force of intensity of...slow down". Mmmmm...I have found a few links featuring the phrase offered above. Here goes link 1 on "Descongelación de alimentos": "1. Descongelación lenta: en frigorífico, agua fría o temperatura ambiente. 2. Descongelación rápida: por calentamiento, cocción, fritura o microondas." Link 2 shows a few more pages using that phrase. I am not sure it's the really correct term for it but that's the idea anyway and I hope that at least it gets you onto the right track. I'll keep searching anyway just in case...Check links. Cheers :-)