Abandonment sensitivity is a symptom of Borderline Personality Disorder (BPD). In the Diagnostic and Statistical Manual of Mental Disorders (DSM), abandonment sensitivity is described as "frantic efforts to avoid real or imagined abandonment." People with BPD can be very sensitive to any cue (real or perceived) that they are being rejected or abandoned. This can include strong reactions to seemingly minor rejections by others (e.g., becoming terrified or enraged when someone cancels plans).
Since feeling rejected triggers such strong emotional reactions in people with BPD, they will often engage in behaviors designed to reduce concerns that they are being abandoned (e.g., frequently calling someone they are in a relationship with to "make sure" that there are no signs of impending abandonment). Unfortunately, this type of behavior may actually create the feared outcome, leading to failed relationships and even greater fears of being abandoned.