What Does Maker and Taker Mean?

Exchange markets consist of participants known as Makers and Takers. Makers provide liquidity by placing buy or sell limit orders on the exchange's order book. Takers, on the other hand, place buy or sell orders that are immediately matched with the existing orders created by the makers. 

For example, a Maker can place an order to sell 20 BTC when the price of BTC reaches 30,000 USD. A taker can match the order by buying BTC at 30,000 USD.