Reprobates' Quarter of The Graveyard

In Far From The Madding Crowd (Chapter 46), the phrase "reprobates quarter of the graveyard" refers to part of a churchyard traditionally reserved for people whom society or the church regarded as morally suspect, disgraced, or outside the full religious acceptance. 

The word reprobate originally meant a person considered rejected by God or morally depraved.  In nineteenth century rural England, a person who took his own life,  criminal, people who led a scandalous life, and unbaptized individuals were viewed as outside the church. All these persons were considered rejected by God.  The body of these persons, when they die were buried in an isolated place away from the common graveyard.

Hardy often uses such expressions to reveal the harsh judgements of society. 

In the context of Fanny Robin's burial, the phrase carries a painful irony.  Fanny is not truly wicked; she is more a victim of circumstances and of sergeant Troy's conduct.  Yet social convention tends to treat a fallen woman as though she belongs among reprobates.  Hardy is criticising this moral double standard, showing how compassion is often absent from public judgement. 

So, the expression means not merely a physical corner of the graveyard, but also society's tendency to  classify and condemn certain people even after death.  Fanny's placement there underscores the tragedy of her fate and the injustice of community's moral assumptions.