Given two pmfs $p$ and $q$ on the same alphabet $\mathscr{X}$, the Jensen-Shannon Divergence is defined as $$D_{JS}(p\|q):=\frac{1}{2}D(p\|\mathcal{M})+\frac{1}{2}D(q\|\mathcal{M})$$ where $$\mathcal{M}(a):=\frac{p(a)+q(a)}{2}$$ # Intuition This is essentially a symmetric version of divergence hence it’s more widely applicable and does not place one distribution as the focal point or reference point.