Bohr radius
An important distinction is that the Bohr radius gives the radius with the maximum radial probability density, not its "expected" radial distance. The expected radial distance is 1.5 times the Bohr radius, as a result of the long tail of the radial wave function. Another important distinction is that in three-dimensional space, the maximum probability density occurs at the location of the nucleus and not at the Bohr radius, whereas the radial probability density peaks at the Bohr radius, i.e. when plotting the probability distribution in its radial dependency.