Definition - What does Polygraph mean?
A polygraph is a device that is supposed to help determine whether or not an individual is lying or telling the truth.
The device works by measuring biological responses to questions and the answers provided by the test subject.
In the context of the law, polygraph evidence is inadmissible in court because it is only believed to be around 90% accurate.
Justipedia explains Polygraph
Despite the fact that polygraphs are not used to provide evidence for courts, they are still commonly used by employers to interview prospective employees. Employers commonly make prospective employees undergo polygraph testing so that they can ask them questions that are very relevant to the field. For example, a law enforcement agency may ask prospective employees about their involvement in any crime in the past.
Until polygraph testing is 100% accurate, it is unlikely to be used as evidence in a trial.