In its most basic meaning, a curse is a prayer asking that a god or similar spirit brings misfortune to someone; an imprecation or execration, the opposite of a blessing. It is also the effective implementation of the god's wrath against the victim of the curse. Other sorts of curses are imposed by magic or witchcraft, such as the evil eye or by the use of voodoo dolls.
Certain objects or places are said to be cursed. Sometimes, the curse was allegedly laid with a purpose; such a curse is supposed to have haunted the archaeologists who excavated the tomb of Pharaoh Tutankhamen; a curse was supposedly pronounced on anyone who violated its precincts by the ancient Egyptian priests. Tecumseh's curse was reputed to cause the deaths in office of Presidents of the United States elected in years divisible by 20 beginning in 1840 (this alleged curse appears to have fallen dormant in 1980, as President Ronald Reagan, elected that year, and President George W. Bush, elected in 2000, have failed to die in office). Other curses seem to have neither motive nor purpose. The Hope diamond is supposed to bear such a curse, and bring misfortune to its owner; like Tecumseh's curse, this alleged curse has been dormant since the diamond became part of the collection of the Smithsonian museum.
Belief in curses is a part of the vague sort of animism, similar to belief in luck, that is a part of folk religion and popular superstition. The deliberate levying of these sorts of curses is a part of the practice of magic, or perhaps lies on the boundaries between magic and religion. Some people claiming to be clairvoyants or practitioners of divination attempt to get money from the gullible by telling them they are under curses that only their apotropaic powers can remove. This is an ancient type of confidence trick familiar to the Egyptians, and a species of fraud, unlawful under the laws of many jurisdictions.
In a broader sense, 'curse' is a loose synonym for blasphemy or profanity.