An inductor resists a change in current that is why it blocks AC. The equation of an inductor is \(\frac{\mathrm{di} }{\mathrm{dt} } = \frac{\mathrm{V} }{\mathrm{L} }\) . If you apply DC across an inductor, it will stabilize to some current flow based on the maximum current available from the current/voltage source. In this mode, the inductor presents very low resistance, so it can be said that it allows DC to pass.