It has no definite meaning. Some say "hot load" refering to a max load for a particular cartridge that is still safe and within limits. Others would say a "hot" load is one that is over maximum and bordering on unsafe.

Stretching what you have instead of just buying a bigger gun is one of the benefits of handloading. The "hot load" bug is mostly centered around the magnum handgun cartridges for some reason. I guess some of us are just recoil junkies...

To me, a "hot load" for your gun would be a .357 case with a 125gr JHP and a max charge of H110/W296. Still safe, but it's definitely going to wake you up when you touch one off, especially from a short barrel.