The letters C in this abbreviation means conjugation of charges, that is each elementary particle has a twin with an opposite charge: antineutrons, electrons, anti electrons, or positrons, and so on.

字母 C 在这缩写中的电荷的轭，即每粒子都有一带相反电荷的孪生体：反中子、电子、反电子或正电子等等。