Concealed Carry Weapons are a category of handguns, small enough to be comfortably holstered underneath clothes, and therefore hidden from view. Generally, CCWs are magazine-fed, automatic pistols, but special revolvers exist in this category as well.
In addition to their small size, engineered CCWs usually lack case protrusions such as beavertails (the metal guard that projects out from below the hammer), or large sights, to avoid snagging the fabric or hems of the clothes they are hidden under. On the other hand, in the case of ordinary handguns, like the SIG P-239, which are then modified into CCW editions, such protrusions are filed down, rounded off, or eliminated altogether. This practice is known as dehorning.
A category of armament pioneered in the early 1920s for plainclothes police officers, CCWs weren't too well known by the general public, until such examples as the Walther PPK saw significant airtime in 1960s movie series like James Bond. In the Gunslinger Girl saga, the most commonly seen CCWs are the SIG P-230/P-232 (used by Triela) and the P-239 Two Tone (used by Henrietta).