What is a buy order?
A buy order is placed when a trader approaches an exchange with the intent to buy a certain asset.
There are several types of buy orders, with the simplest being the market order, which simply says to buy at whatever the current market price is.
There are other types of orders that can specify a price range, or time frame or other factors that must be met in order for the buy order to be triggered and filled.
A buy order is no guarantee that it will be filled. In some cases your conditions are never met and the order expires unfilled.