loophole

A loophole is an ambiguity or inadequacy in a system, such as a law or security, which can be used to circumvent or otherwise avoid the purpose, implied or explicitly stated, of the system.
Originally, the word means an arrowslit, a narrow vertical window in a wall through which an archer could shoot.
Loopholes are distinct from lacunae, although the two terms are often used interchangeably. In a loophole, a law addressing a certain issue exists, but can be legally circumvented due to a technical defect in the law. A lacuna, on the other hand, is a situation whereby no law exists in the first place to address that particular issue.

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