There is no Concealed Carry in the District of Columbia.
Concealed carry is the ability to, legally carry a gun that is not plainly visible. This applies to carrying it on one's person, or inside their vehicle. While many states allow concealed carry of a firearm on one's person with a permit, most do not allow concealed carry in a vehicle, or have strict guidelines on how the gun must be stored.
Most states require the applicant be at least 21 to apply for a permit, along with other requirements unique from state to state. There is a fee invaulved in getting a CCW which varies widly from state to state. Some states honor the concealed carry permit of certain other states (see the Permits Honored section for a complete listing).