Forex Basics: Currency Pairs, Spreads, Rates, Direct vs Cross Quotes, and Margin

Currency Pair Anatomy

Each forex instrument is a currency pair written as ISO‑3 code/ISO‑3 code, e.g. EUR/USD. The left‑hand currency is the base currency, fixed at 1 unit; the right‑hand currency is the quote currency, indicating how many units of the quote are required to buy one unit of the base. If the quote is 1.1200, buying 1 EUR costs 1.1200 USD.

All trading actions (buy or sell) are performed on the base currency.

Classification of Pairs

Major (direct) pairs always contain USD and a major economy currency (EUR, JPY, GBP, CHF, CAD, AUD, NZD). Examples: EUR/USD, USD/JPY, GBP/USD, USD/CHF, USD/CAD, AUD/USD, NZD/USD.

Minor (cross) pairs contain no USD and are formed from two major currencies, e.g. EUR/GBP, GBP/JPY, EUR/JPY, AUD/JPY.

Exotic pairs combine a major currency with an emerging‑market currency, e.g. USD/TRY, USD/MXN, USD/ZAR, USD/SGD.

Pairs that include USD are called direct quotes; those without USD are cross quotes.

Exchange‑Rate Regimes

Floating rates are set entirely by market supply and demand. Major pairs such as GBP/USD react instantly to economic news and central‑bank policy.

Fixed (pegged) rates are maintained by a government or central bank against another currency or a basket. Example: Hong Kong’s linked rate of 7.80 HKD ↔ 1 USD (±0.05).

Margin Mechanics

Margin is the portion of account equity locked by the broker to support leveraged positions; it is released when positions are closed. A standard lot equals 100 000 units of the base currency, allowing control of a large notional amount with a small cash outlay.

Margin Call : triggered when equity falls to a broker‑defined threshold (e.g., 100 % of required margin), prompting the trader to add funds.

Stop‑Out : triggered at a lower equity level (e.g., 50 % or 20 %). The system automatically closes positions, starting with the most losing ones, to prevent a negative balance.

Bid/Ask Spread

Trading platforms display two prices: the Ask (sell price for the broker, buy price for the client) and the Bid (buy price for the broker, sell price for the client). Example for EUR/USD: Ask = 1.10012, Bid = 1.10000. The difference (0.00012 = 1.2 points) is the spread.

Because the client’s buy price is higher than the sell price, opening and immediately closing a position creates a small floating loss.

Slippage

Slippage occurs when the execution price differs from the quoted price. Example: a displayed price of 1.2500 executes at 1.2502, a 2‑point slippage.

Network latency : physical distance and transmission time between the trader’s terminal, broker server, and liquidity pools.

Market volatility : rapid price moves around economic releases (e.g., NFP, central‑bank decisions) or geopolitical events.

Liquidity depth : insufficient order‑book volume at the desired price, especially for large orders.

Slippage can be negative (worse price) or positive (better price) depending on market direction.

Order Types and Their Impact on Slippage

Market Order : goal is immediate fill; price control is very low (fills at best market price); execution certainty is 100 %; slippage risk is high, especially in volatile markets; typical use is fast entry/exit or breakout trading.

Limit Order : goal is to fill at a specified price or better; price control is high (price ≤ limit for a buy); execution is not guaranteed (order may miss); slippage risk is low because no slippage occurs if the order is filled; typical use is position building, precise risk control, or when immediate execution is not required.

Key Takeaways

Understanding the structure of currency pairs, their classification, exchange‑rate regimes, margin mechanics, bid/ask spread, slippage, and order‑type behavior provides the technical foundation needed for analyzing and redesigning foreign‑exchange trading systems.