J Value Definition:

When signal splitting occurs in 1H NMR spectroscopy, the distance (in hertz) between the individual peaks of a signal.

J Value Explained:

For example when protons are attached to one and the same atom such as carbon, a double bond with different groups with no rotation. The protons would group together making a germinal coupling. In the NMR spectrum, the proton’s signals can work with the magnetic field or against, if both have the same peak signal readings they make coupling constants when coupled together.