the.com/redundancy
Two of everything, so the apocalypse only gets to ruin one.
means Having backup parts, people, or systems so a single failure doesn't bring everything crashing down.
from From Latin redundare, to overflow — water flooding back, an excess that spills past what's strictly needed.
Engineering creedTwo is one, one is none.
British twistThere it also means losing your job.
AviationJets carry triple or quadruple critical systems.