Medical Definition of borderline
1: being in an intermediate position or state : not fully classifiable as one thing or its opposite; especially : not quite up to what is usual, standard, or expected <borderline intelligence>
2: exhibiting typical but not altogether conclusive symptoms <a borderline diabetic>
3: of, relating to, being, or exhibiting a behavior pattern typical or suggestive of borderline personality disorder <a borderline patient> <borderline behavior>
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