Dark magic in the Kopavus system has the technical name of “unnatural magic”. However, “dark magic” is generally one of the slang terms for the usage of unnatural magic.
In general, dark magic is only used by a very small percentage of the population, in part due to the general view against it. It’s impossible to be born with it, and because being a user of dark magic allows for far more powerful magic than normal, it’s technically outlawed in the five main kingdoms, as well as their respective colonies. There are even urban legends and other sorts of tales told about dark magicians, lusting for political power or attempting to gain the magical ability to slaughter their enemies.
Very few people use dark magic, although this can also be attributed to how difficult it is to obtain. Almost all, with a few exceptions, are part of a secret society, normally considered a cult to outsiders, has influence all throughout the five kingdoms. When inducting someone new into their groups, they go through a dangerous magical process to break a magical “barrier” that exists around everyone. Those with a stronger barrier generally have weaker magic, and vice versa. By reducing this, they open the user to greater ability, albeit unnaturally. However, this puts the user into a coma for a short period of time, and it’s not uncommon for them to die of malnourishment during this stage, as there’s really not much that can be done to help them. Fortunately, the coma is normally not too long, and due to knowledge increasing, while they may be brought to the brink of death, the death rates have decreased slightly in recent years.
By becoming a dark magician, the users are capable of far greater feats of magic than they normally would be able to do. Because of this in part, the society of dark magicians is able to gain power and knowledge throughout the kingdoms. They have a strict organisation and leadership system.
It’s usually impossible to spot a dark magician without observing their magic. The stronger someone’s magic is at birth, the lighter their natural hair colour, and becoming a dark magician does not influence this. Therefore, by seeing how closely their hair colour and magic levels line up, it can be determined whether or not the person has tampered with their magical ability. Outside of that, only people with the ability to block magic, which finds its effectiveness reduced on dark magicians, and those who can sense magic type and levels are able to tell, although both of these are uncommon abilities and generally would require focus and time or opportunity before saying with certainty whether someone is a dark magician or not.