Susan,

I have been a shooter and reloader for a good 30 years.

Your question is too general. It needs to be more specific, like: what is a hot load for a 38 Special? This round for example has commercial ammo that is +P (extra pressure) and there is also ammo that is +P+ (safe only in new, quality, guns). Cor-Bon for example loads “hot” ammo. That is; they use light bullets pushed to maximum safe pressure for maximum velocity. Also if you reload ammo you use a reloading manual. The manual has a minimum and maximum amount of gun powder that your can use for a cartridge and bullet weight combination. If you load to the maximum then you have a “hot” load. Some reloaders will load above the maximum safe amount of gun powder listed in a reloading manual and that is also called “hot” ammo.

As a general term, related to ammunition, “hot” means that it has the maximum pressure for that cartridge to get the most velocity possible. Energy is mass times velocity squared. That means that a small increase in velocity will give a bigger boost to energy. The more energy: the more powerful the cartridge is.

Their purpose is to get a little extra velocity to get a little extra power.