A term used intort lawto describe an act that is legal but performed improperly.
Generally, a civil defendant will be liable for misfeasance if the defendant owed a duty of care toward the plaintiff, the defendant breached that duty of care by improperly performing a legal act, and the improper performance resulted in harm to the plaintiff.
For example, assume that a janitor is cleaning a restroom in a restaurant. If he leaves the floor wet, he or his employer could be liable for any injuries resulting from the wet floor. This is because the janitor owed a duty of care toward users of the restroom, and he breached that duty by leaving the floor wet.
In theory, misfeasance is distinct from nonfeasance. Nonfeasance is a term that describes a failure to act that results in harm to another party. Misfeasance, by contrast, describes some affirmative act that, though legal, causes harm. In practice, the distinction is confusing and uninstructive. Courts often have difficulty determining whether harm resulted from a failure to act or from an act that was improperly performed.
To illustrate, consider the example of the wet bathroom floor. One court could call a resulting injury the product of misfeasance by focusing on the wetness of the floor. The washing of the floor was legal, but the act of leaving the floor wet was improper. Another court could call a resulting injury the product of nonfeasance by focusing on the janitor's failure to post a warning sign.
Kionka, Edward J. 1988. Torts. St. Paul, Minn.: West.
"Misfeasance." West's Encyclopedia of American Law. . Encyclopedia.com. (September 22, 2017). http://www.encyclopedia.com/law/encyclopedias-almanacs-transcripts-and-maps/misfeasance
"Misfeasance." West's Encyclopedia of American Law. . Retrieved September 22, 2017 from Encyclopedia.com: http://www.encyclopedia.com/law/encyclopedias-almanacs-transcripts-and-maps/misfeasance
"misfeasance." The Concise Oxford Dictionary of English Etymology. . Encyclopedia.com. (September 22, 2017). http://www.encyclopedia.com/humanities/dictionaries-thesauruses-pictures-and-press-releases/misfeasance
"misfeasance." The Concise Oxford Dictionary of English Etymology. . Retrieved September 22, 2017 from Encyclopedia.com: http://www.encyclopedia.com/humanities/dictionaries-thesauruses-pictures-and-press-releases/misfeasance