Definition of Injunction:

“n. (16c.) A court order commanding or preventing an action. To get an injunction, the complainant must show that there is not plain, adequate, & complete remedy at law & that an irreparable injury will result unless the relief is granted. — Also termed writ of injunction, equitable injunction.”

     Excerpt from Howard C. Joyce’s A Treatise on the Law Relating to Injunctions:

      “In a general sense, every order of a court which commands or forbids is an injunction, but in its accepted legal sense, an injunction is a judicial process or mandate operating in personam by which, upon certain established principled of equity, a party is required to do or refrain from doing a particular thing. An injunction has also been defined as a writ framed according to the circumstances of the case, commanding an act which the court regards as essential to justice, or restraining an act, which it esteems contrary to equity & good conscience; as a remedial writ which courts issue for the purpose of enforcing their equity jurisdiction; & as a writ issuing by the order & under the seal of a court of equity.” [2]

Definition of Irreparable-Injury Rule:

“(1969) The principle that equitable relief (such as an injunction) is available only when no adequate legal remedy (such as monetary damages) exists. Although courts continue to cite this rule, they do not usually follow it literally in practice. — Also termed adequacy test.”

      Excerpt from Douglas Laycock, The Death of the Irreparable Injury Rule (1991):

     “The irreparable injury rule has received considerable
scholarly attention. In 1978, Owen Fiss examined the possible reasons for the rule & found them wanting. A vigorous debate over the economic wisdom of applying the rule to specific performance of contracts began about the same time, & soon came to center on the transaction costs of administering the two remedies. Both Fiss & Dan Dobbs have noted that the rule does not seem to be taken very seriously, &in a review of Fiss’s book, I
argued that the definition of adequacy pulls most of the rule’s teeth. The Restatement (Second) of Torts dropped the rule from the blackletter & condemned it as misleading, but replaced it only with a long & unstructured list of factors to be considered… [M}any sophisticated lawyers believe that the rule continues to
reflect a serious preference for legal over equitable remedies.” [3]

Types of Injunctions:

• Anti-Antisuit Injunction – (1988) An injunction prohibiting a litigant subject to the jurisdiction of a local court from seeking in a foreign court to restrain the continuation of a proceeding in the local court.”
• Antisuit Injunction – (1961) An injunction prohibiting a litigant from instituting other, related litigation, usually between the same parties on the same issues.”
• Common Injunction – (18c) Hist. 1. An injunction grantable as an order of course, without reference to the merits, when the defendant failed to appear or
  failed to timely plead, answer, or demur. 2. English law. An injunction issued by a court of equity forbidding enforcement of a common-law judgment. In some
  cases, common law and equity rules differed, which could lead to inconsistent remedies. A court of equity that ensured the equitable rule would prevail by
  issuing a common injunction. Common injunctions were abolished in England by the Iudicature Act of 1873, § 24(5). – Also termed equitable common
  injunction.”
• Ex Parte Injunction – (1854) A preliminary injunction issued after the court has heard from only the moving party. – Also termed temporary restraining order.”
• Headstart Injunction – (1984) Trade secrets. An injunction prohibiting the defendant from using a trade secret for a period of time equal to the time
  between the date of the secret’s theft & the date when the secret became public.  So named since that period is the ‘head start’ the defendant unfairly gained over
  the rest of the industry.”
• Hyperinjunction – (2009) English law. Slang. A superinjunction that expressly applies its bar on discussing the subject matter or even the injunction’s
  existence to journalists, Members of Parliament, and lawyers except for the recipient’s council. * The first known hyperinjunction was issued in 2006. See
  GAG ORDER (1). Cf, superinjunction.”
• Mandatory Injunction – (1843) An injunction that orders an affirmative act or mandates a specified course of conduct. – Also termed affirmative injunction.
  Cf. prohibitory injunction.”
• Permanent Injunction – (1846) An injunction granted after a final hearing on the merits. Despite its name, a permanent injunction does not necessarily last
  forever. – Also termed perpetual injunction; final injunction.”
• Preliminary Injunction – (1828) A temporary injunction issued before or during trial to prevent an irreparable injury from occurring before the court has a chance to decide the case. A preliminary injunction will be issued only after the defendant receives notice and an opportunity to be heard. ~Also termed
  interlocutory injunction; temporar injunction; provisional injunction; injunction pen ente lite. Cf. ex parte injunction; TEMPORARY RESTRAINING ORDER.“
• Preventative Injunction – (1882) An injunction designed to prevent a loss or injury in the future. Cf. reparative injunction.
• Production Injunction – (1994) Trade secrets. A permanent injunction prohibiting specified conduct in a field or activity that the court has found to
  embrace misappropriated trade secrets.
• Prohibitory Injunction – (1843) An injunction that forbids or restrains an act. This is the most common type of injunction. Cf. mandatory injunction.”
• Quia-timet Injunction – [Latin “because he fears”] (1913) An injunction granted to prevent an action that has been threatened but has not yet violated the plaintiff’s rights; See QUIA TIMET.”
• Reparative Injunction – (1955) An injunction requiring the defendant to restore the plaintiff to the position that the plaintiff occupied before the defendant committed a wrong. Cf. preventive injunction.”
• Special Injunction – (18c) Hist. An injunction in which t e prohibition of an act is the only relief ultimately sought, as in prevention of waste or nuisance.
• Superinjunction – (2009) Slang. English law. (2009) A type of gag order that forbids the recipient not just to discuss the subject matter but also to reveal the existence of the injunction itself. * Since Members of Parliament are not restrained by the injunction because of parliamentary privilege, and because parliamentary proceedings may be reported without restriction. the existence and contents of a superinjunction may be made known indirectly. –Also written super-injunction. See GAG ORDER (1),. Cf. Hyperinjunction.
• Use Injunction – Trade secrets. A permanent injunction prohibiting the use of specified information that the court has found to constitute a trade secret.”

References:

[1]: All definitions from: Black’s Law Dictionary Deluxe Tenth Edition by Henry Campbell Black & Editor in Chief Bryan A. Garner. ISBN: 978-0-314-62130-6

[2]: 1 Howard C. Joyce, A Treatise on the Law Relating to
Injunctions § 1, at 2-3 (1909)

[3]: Douglas Laycock, The Death of the Irreparable Injury
Rule 9 (1991)