Unfortunately, the topic of "unwanted firearm discharges" comes up quite often online, either when a news story about such an incident is being discussed, or when a member of a firearm-related forum has an "insert word here" discharge.
The topic can be contentious and is riddled with half truths and misunderstandings. I'm not claiming to be the final source of information on the topic, but I do believe that I have a well-grounded opinion. Now, some people say that there's no such thing as an accidental discharge, and others say there's no such thing as a negligent discharge. I disagree with both camps.
In my opinion, an accidental discharge is the result of a mechanical malfunction. Something is physically wrong with the weapon, specifically, one or more of its internal components.
Also in my opinion, a negligent discharge is the result of a shooter malfunction. Either the person holding/carrying the weapon was not trained in the safe handling of firearms, or the person knowingly ignored said training for some reason. Any external influence that causes the firearm to discharge also falls under the category of negligent discharges. This includes, but is not limited to, allowing the thumb strap of certain holsters to enter the trigger guard of a pistol while reholstering.
The vast majority of "unwanted discharges" are negligent discharges. I don't know how many times I've heard something along the lines of "It was an accident, I didn't mean for it to 'go off'". Intent has no bearing on this. Obviously, both accidental and negligent discharges are unwanted, hence me lumping them in together. Nobody wants for their weapon to have a dangerous malfunction, and nobody wants to "accidentally" shoot someone. Unfortunately, without an element of negligence, large or small, the latter case just doesn't happen.
One other common phrase is "I didn't know the gun was loaded" - that's a sure sign of a negligent discharge. An accidental discharge can occur during the normal, safe handling of a loaded firearm, when all firearms safety rules are being carefully observed, although such incidents are exceedingly rare. An example would be the decocker on surplus CZ-52 pistols, which can cause the weapon to fire when engaged if certain components are worn, or certain weapons that will fire when dropped (it could certainly be argued that dropping a firearm is a form of negligence, however, it is nice to know whether your firearm will discharge or not in the unlikely event that it is dropped). These situations are generally known to the shooting world and appropriate precautions can be taken to mitigate risk. The vast majority of shooters will never encounter a true accidental discharge.
On the other hand, a negligent discharge occurs as a result of the violation of at least one and sometimes two or three safety rules. Every violation of a weapons safety rule is an occurrence of negligence. It doesn't matter if you think the firearm is unloaded - you should always treat it as if it was loaded. This is basic stuff, but it is ignored way too often.
However, not all negligent discharges occur when the shooter chooses to ignore that first rule. As mentioned previously, another common cause is when a pistol is being reholstered. Sometimes, the trigger finger is caught by the holster, and other times, a retention strap can enter the trigger guard. Either case is not the result of a mechanical malfunction of the weapon, but of the negligence of the shooter in failing to ensure that nothing entered the trigger guard.
It can be a personal affront to the person whose negligence caused the discharge - and admitting fault in such a situation can be a hefty blow to a sometimes fragile ego - but identifying and acknowledging the situations by which a negligent discharge can occur will hopefully prevent them from happening again, if not in the first place.