Used to express a deep, almost necessary involvement with an activity or interest that defines someone's happiness or purpose. She lives for her volunteer work, it gives her life meaning.
Pro Tip 2/3
Hyperbolic Emphasis
May be an exaggeration to emphasize strong feelings but doesn't mean it's the only thing they enjoy. He says he lives for coffee, but he also enjoys tea.
Pro Tip 3/3
Personal Identity
Often refers to something that forms a big part of a person's identity or how others recognize them. She lives for fashion; her unique style sets her apart.