Forex positions - open, close, short, long

There are such important terms in forex as "long position", "short position", "close position", "open position".

Position - The amount of currency or security owned or owed by a forex trader or investor.

Long (Position) - A position that was obtained by buying in anticipation of an increase in price.
Open:

Each open position has four major characteristics: You're trading a particular currency pair, you're either long or short the market (you've bought or sold, respectively), the size of the position in increments of 100,000 of the base currency, and an exchange rate at which the position was opened. For example a "EUR/USD, 500, S, 0.9220", means the trader Sold 500,000 Euros for U.S. Dollars at an exchange rate of 0.9220.
Close:

The close rate is the current exchange rate at which the trader can exit the position using a market order. If you're long the market, the current bid will be shown as the close rate. If you're short, the close will reflect the current FX market ask price.
Going short – going long

When you buy a currency, you are said to be “long” in that currency. Long positions are entered into at the offer price. Thus if you are buying one GBP/USD lot quoted at 1.5847/52, then you will buy 100,000 GBP at 1.5852 USD.

When you sell a currency, you are said to be “short” in that currency. Short positions are entered into at the bid price, which is 1.5847 USD in our example.

Because of the symmetry of currency transactions, you are always simultaneously long in one currency and short in another. For example if you exchange 100,000 GBP for USD you are short in sterling and long in US dollars.
Closing out

An open position is one that is live and ongoing. As long as the position is open, its value will fluctuate in accordance with the exchange rate in the market. Any profits and losses will exist on paper only and will be reflected in your margin account.

To close out your position, you conduct an equal and opposite trade in the same currency pair. For example, if you have gone long in one lot of GBP/USD (at the prevailing offer price) you can close out that position by subsequently going short in one GBP/USD lot (at the prevailing bid price).

Your opening and closing trades must the conducted through the same intermediary. You cannot open a GBP/USD position with Broker A and close it out through Broker B.