Let $f:M\to M$ be a diffeomorphism on a compact riemannian manifold $M$.In the definition of a hyperbolic set we know that for all $x\in M$ there is a splitting of tangent space

$T_xM=E^s(x)\oplus E^u(x)$

I want to know what is the definition of angle between $E^s(x)$ and $E^u(x)$?