  In this work, we obtain quasibound states of a massive scalar around the Kerr
black hole.
  A massive scalar propagating around the Kerr black hole induces the
far-region potential with either a trapping well or a tiny well, which produces
a peak of resonance or a bound state in the far-region. The former represents
superradiant instability, while the latter could accommodate superradiant
instability via a positive $\omega_I$. If the scalar's energy is really
quantized around a tiny well, an ultralight boson could be expressed in terms
of a hydrogen-like bound state, leading to a gravitational atom when
incorporating superradiant instability. If there are no wells outside the outer
horizon, their far-region wave functions represent purely bound state without
node. Finally, we discriminate between superradiant instability and stability.
