Generally, an order is explained as an instruction to buy or sell. Market orders are instructions to buy or sell immediately at the current prices. This is the preferred transaction order employed when the need to ensure a transaction occurs is more significant than consideration of execution price. A market order happens when buy order equates sell order. That is, a market order is successful only when there are willing buyer and seller of an asset at a particular price.
In cases of large orders in a fast moving market, a market order is filled at the best price existing at the time. If, however, the order isn't filled in one transaction, it will continue to do so at the next best existing price which may result in a single order being filled at different prices.
A market order is considered as the easiest and fastest way to buy or sell an asset.