Malpractice is an action at law to recover damages against a professional, such as a physician, who fails to meet the level of care for a patient expected of an ordinarily competent professional. It is similar to the tort of negligence, except that in most cases the standard of care cannot be proved except through the use of expert evidence.
It is not enough for a patient to suffer an adverse affect from treatment or not to not be diagnosed properly in order to support a finding of malpractice. That patient must prove that a course of treatment or correct diagnosis would have been found by an ordinarily skilled physician without benefit of hindsight. In addition, a medical error does not necessarily create a finding of negligence. For example, when Eric Foreman gave the patient in Histories a drug she was allergic to, it was not malpractice as the patient's medical history was not yet available and the patient had not warned him of drug allergies.
Gregory House is infamous for being sued for malpractice. However, it should be noted that diagnostics is the field most likely to result in a finding of malpractice against a physician. Nevertheless, House was sued for malpractice several times before he joined Princeton-Plainsboro Teaching Hospital, and has faced several lawsuits during the course of the series.
In Paternity, House realizes that his clinic patient, John Funsten, has come to Princeton-Plainsboro because he has sued every other doctor between his hometown and Princeton. House treats him anyway and Funsten comes the next day to serve him with a malpractice suit. To torture Funsten, House tells him that he has tested positive for gonorrhea and he has to tell Funsten's wife so she can get treatment. Funsten thinks he is bluffing, but House tells him to get another test, realizing Funsten won't be able to. As the medical records are now evidence in the civil suit, House refuses to release them.