1. a boundary line between two areas or countries

1. very close to being unacceptable or to reaching a particular condition
2. only just acceptable in quality or standard

Examples

• The fence marks the borderline between the two properties.
• His behavior was borderline inappropriate for the workplace.
• She received a borderline passing grade on the exam.
• The patient’s condition is borderline critical.
• That joke was borderline offensive.
• The restaurant’s food quality is borderline acceptable.
• We walked along the borderline between the two states.