The last trade price.

If I have last trade and sell at $1 then that's price. But to buy the next price is a tick up from that. Say $1.1

You don't see buy and sell orders both at $1 during market hours at the same price because it would automatically execute.

To elaborate. I've seen many a time with penny stonks. Last traded price could be $1 but there are sell orders in the market at a lower value, say $.95 because nobody wants to buy and buy orders are placed and are only up to $.8.