[MIT from the Schroedinger's Cat thought-experiment in quantum physics] n. A design or implementation bug in a program which doesn't manifest until someone reading source or using the program in an unusual way notices that it never should have worked, at which point the program promptly stops working for everybody until fixed. Though this sounds impossible, it happens; some programs have harbored latent schroedinbugs for years. Compare heisenbug, Bohr bug, mandelbug.