  Outer resonances are studied as one type of quasinormal modes in
two-dimensional dielectric cavities with refractive index $n>1$. The outer
resonances can be verified as the resonances which survive only outside the
cavity in the small opening limit of the dielectric disk. We have confirmed
that the outer resonances universally exist in deformed cavities irrespective
of the geometry of cavity and they split into nearly degenerate states in
slightly deformed cavity. Also we pointed out that the effective potential
analogy is inapplicable to the description of outer resonances. Since most
outer resonances in the dielectric cavities have quite high leakages, they
would affect to the broad background in the density of states. Especially, for
TE polarization case, relatively low-leaky outer resonances exist and it
presents the possibility that they can interact with the inner resonances and
affect lasing modes.
