One of the oldest torts, a nuisance is any condition or activity that interferes with a person's "quiet enjoyment" of his or her property. The word comes from the Latin nocere (to hurt), from which we get such related words as annoyance, noise, and noxious. A public nuisance is an unreasonable interference with the public's health, safety, peace or convenience.
The doctrine of nuisance gives rise to the delightfully oxymoronic attractive nuisance, refers to dangerous conditions that might be positively inviting to certain people (think children wandering on to a construction site). Attractive nuisance is sort of like "willful negligence" -- only lawyers could come up with these terms.