A currency pair is the quotation of the relative value of a currency unit against the unit of another currency in the foreign exchange market. The currency that is used as the reference is called the counter currency or quote currency and the currency that is quoted in relation is called the base currency or transaction currency.
Currency pairs are sometimes then written by concatenating the ISO currency codes (ISO 4217) of the base currency and the counter currency, separating them with a slash character. Often the slash character is omitted. A widely traded currency pair is the relation of the euro against the US dollar, designated as EUR/USD. The quotation EUR/USD 1.2500 means that one euro is exchanged for 1.2500 US dollars. Here, EUR is the base currency and USD is the counter currency.
Syntax and quotation 
Currency quotations use the abbreviations for currencies that are prescribed by the International Organization for Standardization (ISO) in standard ISO 4217. The major currencies and their designation in the foreign exchange market are the US dollar (USD), euro (EUR), Japanese yen (JPY), British pound (GBP), Australian dollar (AUD), Canadian dollar (CAD), and the Swiss franc (CHF).
As has been mentioned previously, the quotation EUR/USD 1.2500 means that one euro is exchanged for 1.2500 US dollars. If the quote changes from EUR/USD 1.2500 to 1.2510, the euro has increased in relative value, because either the dollar buying strength has weakened or the euro has strengthened, or both. On the other hand, if the EUR/USD quote changes from 1.2500 to 1.2490 the euro is relatively weaker than the dollar.
Base currency 
|Rank||Currency||ISO 4217 code
| % daily share
|United States dollar||
|Hong Kong dollar||
|New Zealand dollar||
|South Korean won||
The rules for formulating standard currency pair notations result from accepted priorities attributed to each currency.
From its inception in 1999 and as stipulated by the European Central Bank, the euro has first precedence as a base currency. Therefore, all currency pairs involving it should use it as their base, listed first. For example, the US dollar and euro exchange rate is identified as EUR/USD.
Although there is no standards-setting body or ruling organization, the established priority ranking of the major currencies is:
- Pound sterling
- Australian dollar
- New Zealand dollar
- United States dollar
- Canadian dollar
- Swiss franc
- Japanese yen
Historically, this was established by a ranking according to the relative values of the currencies with respect to each other, but the introduction of the euro and other market factors have broken the original price rankings.
Other currencies (the Minors) are generally quoted against one of the major currencies. These pairs are also referred to as currency crosses, or simply crosses. The most common crosses are EUR, JPY, and GBP crosses.
The term base currency in the foreign exchange field is also used as the accounting currency by banks, and is usually the domestic currency. For example, a British bank may use GBP as a base currency for accounting, because all profits and losses are converted to the sterling. If a EUR/USD position is closed out with a profit in USD by a British bank, then the rate-to-base will be expressed as a GBP/USD rate. This ambiguity leads many market participants to use the expressions currency 1 (CCY1) and currency 2 (CCY2), where one unit of CCY1 equals the quoted number of units of CCY2.
The Majors 
The most traded pairs of currencies in the world are called the Majors. They constitute the largest share of the foreign exchange market, about 85%, and therefore they exhibit high market liquidity.
The Majors are: EUR/USD, USD/JPY, GBP/USD, AUD/USD, USD/CHF and USD/CAD.
In everyday foreign exchange market trading and news reporting, the currency pairs are often referred to by nicknames rather than their symbolic nomenclature. These are often reminiscent of national or geographic connotations. The GBP/USD pairing is known by traders as cable (also the cable), which has its origins from the time when a communications cable under the Atlantic Ocean synchronized the GBP/USD quote between the London and New York markets. The following nicknames are common: Fiber for EUR/USD, Chunnel for EUR/GBP, Loonie and The Funds for USD/CAD, Aussie for AUD/USD, Guppy for GBP/JPY, Yuppy for EUR/JPY, and Kiwi for the New Zealand Dollar NZD/USD pairing. New innovations include Barney for USD/RUB and Betty for EUR/RUB after the fictional characters the Rubbles in The Flintstones. Nicknames vary between the trading centers in New York, London, and Tokyo.
Cross pairs 
The currency pairs that do not involve the US dollar are called cross currency pairs, such as GBP/JPY. Pairs that involve the euro are often called euro crosses, such as EUR/GBP. There are many local sites providing these types of local currency crosses
Currencies are traded in fixed contract sizes, specifically called lot sizes, or multiples thereof. The standard lot size is 100,000 units of the base currency. Many retail trading firms also offer 10,000-unit (mini lot) trading accounts and a few even 1,000-unit (micro lot).
The officially quoted rate is a spot price. In a trading market however, currencies are offered for sale at an offering price (the ask price), and traders looking to buy a position seek to do so at their bid price, which is always lower or equal to the asking price. This price differential is known as the spread. For example, if the quotation of EUR/USD is 1.3607/1.3609, then the spread is USD 0.0002, or 2 pips. In general, markets with high liquidity exhibit smaller spreads than less frequently traded markets.
The spread offered to a retail customer with an account at a brokerage firm, rather than a large international forex market maker, is larger and varies between brokerages. Brokerages typically increase the spread they receive from their market providers as compensation for their service to the end customer, rather than charge a transaction fee. A bureau de change usually has spreads that are even larger.
Example: consider EUR / USD currency pair EUR / USD – 1.33 Base currency/quote currency
In the above case, someone buying 1 EUR will have to pay 1.33 USD; conversely one selling 1 EUR will receive 1.33 USD (assuming no FX spread). Forex traders buy EUR / USD pair if they believe that the Euro would increase in value relative to the US dollar, buying EUR / USD pair; this way is called going long on the pair; conversely, would sell EUR / USD pair, called going short on the pair, if they believe the value of the Euro will go down relative to the US dollar. A pair is depicted only one way and never reversed for the purpose of a trade, but a buy or sell function is used at initiation of a trade. Buy a pair if bullish on the first position as compared to the second of the pair; conversely, sell if bearish on the first as compared to the second.
See also 
- "World’s Most Traded Currencies By Value 2012". www.therichest.org. Retrieved 9 March 2013.
- "Report on global foreign exchange market activity in 2010" (PDF). Triennial Central Bank Survey. Basel, Switzerland: Bank for International Settlements. December 2010. p. 12. Retrieved 2 May 2011.
- The total sum is 200% because each currency trade always involves a currency pair.
- Heath, Alex; Upper, Christian; Gallardo, Paola; Mesny, Philippe; Mallo, Carlos (December 2007), Triennial Central Bank Survey of Foreign Exchange and Derivatives Market Activity in 2007, Bank for International Settlements, p. 10, ISBN 92-9197-750-0, retrieved 6 October 2009
- Currency pairs: what Forex traders should know
-  FXDD "Dynamics of Currency Pairs", fxdd.co, published 30 June 2012, retrieved 7 November 2012