Question: if the price is literally zero, does that mean it can it be purchased for $0, that it's not for sale, or that there are literally no requests to buy it so the price can't be measured?
There some sells at the minimum price of $0.0001. But nobody is actually buying them. There is no room in the order book for buys. No trading is taking place.
Some stock APIs report this as $0.00, others report it as $0.0001. Both views are correct, you could buy some shares shares at $0.0001, but you can't sell any.
So you could come in, place a bid at 0.025 and the updated OB would be like 0.025x1/0.05x25. If there's any autoquoters from the adversaries, then ok immediately they might throw some more offers up at like 0.045x100, since the interpretation of some bids coming in means that they can fill the orders at the tighter spread
If it could be purchased for $0, only the first stock would cost $0, and the price would then rise, but how would we calculate the price increase for a stock purchased at $0 that is now worth $0.1? So that's not it.
If it were not for sale, why would it be listed?
I think it's the third, and I'd further guess that any bid for the stock will be accepted, thus setting the price.
In case it’s not clear: I only know the price is what I pay for it. I don’t fully understand where it comes from.
Most prices we see on tickers are the lowest asks, I believe.
So doesn't that essentially mean that at the point of measurement—that is, a trade occurring—the price is both lowest ask and highest bid?
Instantaneously afterward, the highest remaining bid will be below the lowest ask.
When anyone talks about "the price" of a stock it is an approximation of some sort. Probably they mean the last traded price; maybe the midpoint (bid+ask)/2; maybe the symbol is in the middle of an auction and they mean the auction clearing price.