 Spin singlet state

The two-spin singlet isSpin measurements along axes $\mathbf{a}$ and $\mathbf{b}$ have correlation $E(\mathbf{a},\mathbf{b})=-\mathbf{a}\cdot \mathbf{b}$, and equal axes give perfect anticorrelation.

This is the spin-one-half singlet state, an example of an angular momentum singlet state. The general singlet condition is zero total angular momentum, not the choice of a particular two-qubit Bell basis.