背井离乡 literally means 'to turn one's back on the well and leave the hometown.' In traditional Chinese communities, the village well was a central, symbolic landmark representing home, community, and ancestral roots. 'Well' (井) here stands metonymically for one’s native place; 'leaving the hometown' (离乡) completes the image of total departure. Together, the idiom conveys the deep emotional weight and hardship of being forced to abandon one’s homeland—often due to war, famine, poverty, or political upheaval.

This is a formal, literary expression commonly found in historical narratives, literature, and news reports about migration or displacement. It carries strong connotations of loss, nostalgia, and sacrifice—not mere relocation, but a wrenching severance from identity and belonging. While it can describe voluntary moves, its emotional resonance is strongest when the departure is involuntary and sorrowful.