In trading financial markets you can typically go ‘Long’ or ‘Short’ meaning to Buy or to Sell a particular instrument/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: Please note that the BID price only is used to draw charts on the MT4 Platform.