In Wikipedia, this formula is used to show the definition of position vectors in all three coordinate systems: position vectors. In spherical coordinates, the position vector is defined as:
$\vec{r}(r,\theta,\phi)=r(t)\hat{e}_r(\theta(t),\phi(t))$
But I don't understand what the comma means. $\hat{e}_r$ is the radial unit vector.
It is functional notation. It means that $\hat{e}_{r}$ is a function depending on two variables: $\theta$ and $\phi$, which in turn depend on $t$.
That is because the basis vector $\hat{e}_{r}$ always points outwards from the origin, so when you change $\theta$ or $\phi$ the vector cannot stay constant.