line 666 [from Christian eschatological myth] n.
The notional line of source at which a program fails for obscure reasons, implying either that somebody is out to get it (when you are the programmer), or that it richly deserves to be so gotten (when you are not). "It works when I trace through it, but seems to crash on line 666 when I run it." "What happens is that whenever a large batch comes through, mmdf dies on the Line of the Beast. Probably some twit hardcoded a buffer size."