Biological and
Chemical Weapon, indicating
poison gas and
germ weapons, etc. Called such because "B" and "C" are the first letters of "
Biological" and "
Chemical". In episode 25' "Air",
Shigeru Aoba feared that the
JSSDF might use BC weapons.
Source: The End of Evangelion : Glossary contained within The End of Evangelion - Theatrical Program.