In trading financial markets you can typically go ‘Long’, or ‘Short’ meaning to Buy, or to Sell a particular instrument or currency pair. For easy reference:
Buy = Long.
Sell = Short.
By going ‘Long’, or ‘Buying’, you are ‘Buying’ the first currency quoted in the pair, and ‘Selling’ the second currency of the pair. ‘Long’ positions are ‘Opened’ at the ‘Ask’ price and ‘Closed’ at the ‘Bid’. By going ‘Short, or ‘Selling, you are ‘Selling’ the first currency quoted in the pair, and ‘Buying the second currency of the pair. Short Positions are ‘Opened’ at the ‘Bid’ price and ‘Closed’ at the ‘Ask’. For Short Positions note that the BID price only is used to draw charts on the MT4 Platform.