Sorcery refers to the use of magic for harm.
Most tales of sorcery stem from wizards’ own attempts to keep people from bothering them too often. These stories serve to keep even their own communities at a respectful distance. Neighboring communities come to consider them dangerous sorcerers. This threat helps keep the peace, too, as neighbors have even more reason not to go to war with one another. It does produce a good bit of tension, though, as each community regards their own magical specialist as an eccentric but ultimately benign person, but each neighboring community harbors someone who seems like an evil sorcerer.
A wizard can, of course, at any time use her magic for evil ends. Knowledge of herbal medicine includes knowledge of poison and its use. She can use knowledge to blackmail or coerce as easily as to help. She can use magic to harm, or even to kill, just as she can use it to heal. Most wizards face at least the rumor that they’ve done precisely that, even if they never have. Many wizards will not deny such rumors, helping to build their legend, and at the same time raising the fear that any wizard might also practice sorcery.
These stories only hold such power, though, because some individuals really do devote themselves to using magic to harm and kill others. These people use poisons, ritual murder, dark magic, and human sacrifice to destroy their enemies and spread terror. Though quite rare, their acts create such terror that wizards can manipulate and capitalize on that fear even when no one has seen any sign of true sorcery in a generation.
Of course, dealing with such fears involves quite a bit of danger of its own, as those fears can grow uncontrollable, and the wizards who tried to manipulate them may face a backlash, false accusations, and angry people seeking vengeance against them.
When true sorcerers do appear, wizards often lead the efforts to find them and stop them. Many wizards earn great respect from their efforts to combat sorcerers, and some unscrupulous wizards do occasionally try to frame their rivals so that they can pursue them as a sorcerer.
On the whole, though, these things happen only rarely. For the most part, the tension of mystery and low-level fear holds, giving wizards the space they need to do their work and keeping everyone else slightly on edge around them.