What’s special about the last two weeks? Or is this someone trying out the poll creation feature on HN?
It's a fancy way of saying "The unusual depressive episode (which can be normal) has lasted at least two weeks (not as normal)". How that exact number was determined I'm not sure (though it was the APA), but that's the standard everyone follows.
EDIT: I believe a variation of this question is standard as part of the PHQ-9 which is a screening/benchmark quick self-assessment for depression.