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 intent, implied or explicitly stated, of the system. Loopholes are searched for and used strategically in a variety of circumstances, including taxes, elections, politics, the criminal justice system, or in breaches of security, or a response to one's civil liberties.Loopholes are distinct from lacunae, although the two terms are often used interchangeably. In a loophole, a law addressing a certain issue exists, but the law can be legally circumvented due to a technical defect in the said law. A lacuna, on the other hand, is a situation whereby no law exists in the first place to address that particular issue.Historically, arrow slits were narrow vertical windows from which castle defenders launched arrows from a sheltered position, and were also referred to as "loopholes". Thus a loophole in a law often contravenes the intent of the law without technically breaking it, much as the small slit window in a castle wall is a small opening in a seemingly impenetrable defensive measure that lets the defender gain the unfair advantage of being able to fire without easily being fired back upon. For example, in some places, one may avoid paying taxes to the jurisdiction by forming a second residence in another location, or a commercial property can be built in a residential zone if it is made also for residential use.[citation needed]In a security system, the one who breaches the system (such as an inmate escaping from prison) exploits the loophole during the breach. Such weaknesses are often studied in advance by the violator, who spends time observing and learning the routine of the system and sometimes conducts surreptitious tests until such a loophole can be found.