*Blackmail is an act of coercion using the threat of revealing or publicizing either substantially true or false information about a person or people unless certain demands are met. It is often damaging information, and may be revealed to family members or associates rather than to the general public. It may involve using threats of physical, mental or emotional harm, or of criminal prosecution, against the victim or someone close to the victim.[1][2] It is normally carried out for personal gain, most commonly of position, money, or property.[1][3][4][5] It is also used, sometimes by state agencies, to exert influence; this was a common Soviet practice, so much so that the term "kompromat", transliterated from Russian, is often used for compromising material used to exert control.

Blackmail may also be considered a form of extortion.[1] Although the two are generally synonymous, extortion is the taking of personal property by threat of future harm.[6] Blackmail is the use of threat to prevent another from engaging in a lawful occupation and writing libelous letters or letters that provoke a breach of the peace, as well as use of intimidation for purposes of collecting an unpaid debt.*

*Extortion is the practice of obtaining benefit through coercion. In most jurisdictions it is likely to constitute a criminal offense; the bulk of this article deals with such cases. Robbery is the simplest and most common form of extortion, although making unfounded threats in order to obtain an unfair business advantage is also a form of extortion.

Extortion is sometimes called the "protection racket" because the racketeers often phrase their demands as payment for "protection" from (real or hypothetical) threats from unspecified other parties; though often, and almost always, such "protection" is simply abstinence of harm from the same party, and such is implied in the "protection" offer. Extortion is commonly practiced by organized crime. In some jurisdictions, actually obtaining the benefit is not required to commit the offense, and making a threat of violence which refers to a requirement of a payment of money or property to halt future violence is sufficient to commit the offense.[1] Exaction refers not only to extortion or the demanding and obtaining of something through force,[2] but additionally, in its formal definition, means the infliction of something such as pain and suffering or making somebody endure something unpleasant.[3]

The term extortion is often used metaphorically to refer to usury or to price-gouging, though neither is legally considered extortion. It is also often used loosely to refer to everyday situations where one person feels indebted against their will, to another, in order to receive an essential service or avoid legal consequences. Neither extortion nor blackmail requires a threat of a criminal act, such as violence, merely a threat used to elicit actions, money, or property from the object of the extortion. Such threats include the filing of reports (true or not) of criminal behavior to the police, revelation of damaging facts (such as pictures of the object of the extortion in a compromising position), etc.[1]*

See synonyms for ultimatum on Thesaurus.com
noun, plural ul·ti·ma·tums, ul·ti·ma·ta [uhl-tuh-mey-tuh, -mah-].
a final, uncompromising demand or set of terms issued by a party to a dispute, the rejection of which may lead to a severance of relations or to the use of force.