(Power Cable) The cable used to supply electric power to the Evangelion from an external source because the Eva has a very short active time as a weapon. This cable could be considered the Eva's weak point. For this reason, the JSSDF units, during their attack on NERV HQ, were instructed to concentrate their firepower on the umbilical cable (which they called the power cable). Incidentally, "umbilical cable (cord)" means the blood vessels which extend from baby's navel to the placenta of its mother's womb. Thus, like a baby receives nutrients through this umbilical cord, the Eva receives electric power through the umbilical cable.

Source: The End of Evangelion : Glossary contained within The End of Evangelion - Theatrical Program.