LCL is a yellow-tinted, translucent liquid used to mentally link a pilot with the Evangelion and supply oxygen directly to the lungs when breathed, similar to liquid breathing. Its properties can be altered when it is electrically charged; this includes turning the liquid colorless. It may also help in protecting a pilot from mental attacks and physical shocks. LCL may also be compared to the amniotic fluid in the mother's womb; many of the mother references that the main character has in the story take place in LCL. Shinji mentions that the cockpit smells of blood when filled with LCL; this is because LCL is the blood of Lilith, the captured second Angel held in Terminal Dogma. This blood may come from the exit wound that the Lance of Longinus made in Lilith's back, despite the lack of similar bleeding from the entry wound. Also visible briefly are several tubes coming out of the back of Lilith's head marked "LCL 1" and "LCL 2" etc. The "dossier" sections of the manga claim that LCL stands for Link Connect Liquid, but this definition was denied in the Red Cross Book.
In The End of Evangelion, it is shown that all humans are composed of LCL, and only given form as separate entities by their own individual AT Fields. Hence, when an individual's AT Field collapses, the body formed by said AT Field dissolves back into LCL