The bid is the highest price of all open buy orders. If you're selling, this is the maximum price you can make a sell order for and have your order instantly filled.

The ask is the lowest price of all open sell orders. If you're buying, this is the minimum price you can make a buy order for and have your order instantly filled.

You "lift the ask"(what you as a buyer are able to buy at), and "hit/slam the bid"( what you as a seller can sell at)

Bid is latest buy order. Ask/Offer is latest sell order.

Many exchanges have the “maker-taker” model. If you add liquidity to the order book, you are paid by the Exchange. If you take liquidity away from the order book, you pay the Exchange.