Correctness

A computer program can be completely correct, it can be correct except in some edge cases, it can be approximately correct, or it can be flat-out wrong.

A statistical model can be kind of ok but a little wrong, or it can be a lot wrong. Except in some rare cases, it can’t be correct.

An iterative computation such as a Stan fit can have approximately converged, or it can be far from convergence. Except in some rare cases, it will never completely converge.