1. A quantum state for which one of a pair of conjugate variables, which cannot simultaneously possess definite values according to the Heisenberg uncertainty principle, is specified more accurately than in the vacuum state, at the expense of increasing the uncertainty in the value of the other variable.

2. A quantum state in which one of a pair of conjugate variables is specified more accurately than in the vacuum state, and the product of the uncertainties of the conjugate variables is the minimum allowed by the Heisenberg uncertainty principle.