All tools have a handle. This is the part of the tool that is held by the user when using the business end to some purpose.
The business end is the part that does the work, for example the tip of a screwdriver, or the pincer of a Vise-Grip™. All tools have a business end. In some cases a tool has more than one part that does work, for example a claw hammer has the blunt flat part to drive nails and the claw to remove them. In this case, the part that performs the primary function of the tool is considered to be the business end, i.e. the blunt flat part of the hammer. You never want to get your hands near the business end when using the tool.
Some tools have also have an end called the "dumb end". The dumb end of a tool is the part that you hit with a hammer or sledgehammer to make it do its job1. Examples include the chisel and the pickle fork (the automotive tool, not the dainty serving utensil). The business end of a chisel is the wedged part. The handle is the shaft. The dumb end is the flat end opposite the wedged part. It is called the dumb end because it requires the least amount of intelligence to use: just hit it real good (try not to smash your thumb).
The vast majority of problems with tools are operator error, and the vast majority of operator errors fall into one of two categories.
- Using the wrong tool for the job
- Using a handle as a dumb end
Many tools do not have a dumb end. Screwdrivers are the most abused in this fashion, as people attempt to use one as a chisel2. Wrench handles are also sometimes hit on the side to loosen tight bolts. The problem is that these tools were not designed to be hit with a hammer - a proper dumb end is made of thick, hard steel that will not crack or severely deform when struck (although some mushrooming is normal). The plastic handle of a screwdriver won't stand up to that kind of abuse for long before cracking, and the handle of a wrench will likewise deform, weakening the whole tool.
1. There is one exception. The dumb end of a retractable tape measure is the 0" end, this is the part that your assistant holds in place for you on the other side of the thing you want to measure. Again, so called because it takes very little intelligence to perform this job successfully.
2. Note, however, that there are screwdrivers designed to be used in this manner. They are easily identifiable by a thick metal circle at the base of the handle. Never use this kind of screwdriver for electrical work, as there may be a conductive path between the tip and the dumb end.