Boats are usually afloat. If they suddenly stop being afloat the situation could be hazardous to the health of anyone onboard.
As any idiot could guess on the first of three guesses, afloat means floating or at sea. That will give the fortunate idiot some time off rather than having to stick around and make the other two guesses.
If you don’t know what afloat means I suggest you don’t go out in deep water because, out there, if you’re not floating, swimming or treading water, you’re drowning. And if you’re ignorant about floating, you’ll probably be ignorant about swimming and treading water too.
If you also don’t know what drowning means, suffice it to say that it’s not something you want to do.
Afloat can also be used analogously. In this case, it usually refers to someone’s financial position and means the same thing as keeping one’s head above water.
Note: No water is involved in this sense of the word, but it does mean that you are liquid. Again, in this sense of the word, liquid doesn’t have anything to do with fluids, but rather cash flows. This sense of afloat means roughly the same thing as one of the senses of the word solvent. Not, mind you, solvent as in a liquid in which something is dissolved, but rather solvent in a financial sense.
This isn’t helping at all, is it? In this usage of the word, afloat means that you aren’t carrying any debt that you can’t afford to carry. In which case, can you loan me a few bucks?