What YOLO Means

Much as I hate acronyms, one that has wedged its way into common parlance is YOLO. It stands for You Only Live Once. What it means is open to interpretation — by me at least.
Is YOLO a mindset, a lifestyle, or a philosophy? It’s a slippery concept, one that can mean many things to many people. I can think of at least four different ways it is used, some of which I can see as being good.