A longer definition, since I'm confined to a character count in the description, per the introduction to her book:

"This book argues that there is a central thread in the tragic tradition that is concerned not with dying too early but with living too long, or "overliving." Lives do not always end at the expected time. Sometimes people go on living even after the moment when they or others feel they should have died. Prolonged old age is one way in which life may seem to go on too long. But even young people may feel that they ought already to have died, when they live on after extraordinary loss. Sophocles, Euripides, Seneca, Shakespeare, and Milton were all concerned with the problem of overliving. Each of these writers presents a character who experiences an apparently intolerable sense of suffering and loss, and feels that he has lived too long but, nevertheless, decides to resist suicide. The sense that the central character "should" have died generates an uneasy feeling in the audience or reader that the text itself "should" have ended. These texts therefore challenge Aristotelian notions of tragic structure, in that they go on after the expected moment of ending. Each writer in the tradition tries to contain or suppress the problem, often by suggesting that from some larger cosmic, historical, or divine perspective, the character's life has not, after all, gone on too long. But these strategies are often not entirely successful. Tragedies of overliving disturb the audience or reader by reminding us that life may feel too long and endings may seem to have come too late.

I take the term "overliving" from Milton, whose Adam asks, after the Fall:

Why do I overlive, Why am I mocked with death, and lengthened out To deathless pain? (Paradise Last 10.773-75)."