Hot Wrench is a term for a destructive method of removing stubborn nuts and bolts, also known as Gas Axe for bigger jobs.
It is sometimes possible to release a seized thread by the gentle application of heat from an Oxy/Acetylene torch. This may be sufficient to remove the offending Nut/Bolt, but the heating affects the temper of the steel rending the item un-reusable. If it doesn't loosen it up, hitting the Oxy and melting the nut off will certainly remove it, but it may damage the surrounding material, or even make it harder to remove the bolt/stud due to slag.
Hot Wench is something entirely different.