Irregularity

A defect, failure, or mistake in a legal proceeding or lawsuit; a departure from a prescribed rule or regulation.

An irregularity is not an unlawful act, however, in certain instances, it is sufficiently serious to render a lawsuit invalid. For example, a number of states have statutes that require the appointment of a guardian to represent the interests of a child who is being sued. The failure to do so is an irregularity that can be used as a ground for invalidating and setting aside a judgment entered against the child.

In other cases, however, the flaw might be a simple Harmless Error that can be easily rectified, and, therefore, does not render the proceeding invalid.

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IRREGULARITY, practice. The doing or not doing that in the conduct of a suit at law, which, conformably with the practice of the court, ought or ought not to be done.
     2. A party entitled to complain of irregularity, should except to it previously to taking any step by him in the cause; Lofft. 323, 333; because the taking of any such step is a waiver of any irregularity. 1 Bos. k Phil. 342; 2 Smith's R. 391; 1 Taunt. R. 58; 2 Taunt. R. 243; 3 East, R. 547; 2 New R. 509; 2 Wils. R. 380.
     3. The court will, on motion, set aside proceedings for irregularity. On setting aside a judgment and execution for irregularity, they have power to impose terms on the defendant, and will restrain him from bringing an action of trespass, unless a strong case of damage appears. 1 Chit. R. 133, n.; and see Baldw. R. 246. Vide 3 Chit. Pr. 509; and Regular and Irregular Process.
     4. In the canon law, this term is used to signify any impediment which prevents a man from taking holy orders.