Two measures $\mu$ and $\nu$ in a measurable space $(\Omega,\mathcal{A})$ are called singular if there exist two disjoint sets $A$ and $B$ in $\mathcal{A}$ such that $A\cup B =\Omega$ and $\mu(B)=\nu(A) = 0$ This is denoted by $\mu\perp\nu$