- A line that establishes or marks a border.
- An indefinite area intermediate between two qualities or conditions: The borderline between love and hate is often thin.
- Verging on a given quality or condition: borderline poverty.
- Of a questionable nature or quality: an applicant with borderline qualifications.
- Psychology Relating to any phenomenon that is intermediate between two groups and not clearly categorized in either group: a borderline state showing the characteristics of both neurotic and psychotic reactions.
- Relating to a condition characterized by a pattern of instability in mood, interpersonal relations, and self-image, and manifested by self-destructive, impulsive, and inconsistent behavior: the borderline syndrome.