What it means
EUR/USD is the world's most liquid FX pair, accounting for roughly 25% of all FX volume. Spread on a good ECN broker during London-NY overlap is 0.0-0.3 pip. The pair is direct USD-quoted (USD on the right), so pip value is a constant $10/pip per standard lot. Most of the FX news cycle is implicitly EUR/USD news because the pair is the cleanest expression of US-vs-Europe macro divergence.
Why it matters
Every FX strategy benchmarks against EUR/USD because it's the cheapest pair to trade and the most documented. Strategy that works on EUR/USD may transfer to other majors with cost adjustment; strategy that fails on EUR/USD almost certainly fails on minors and exotics where costs are higher.
How to use it
Start every FX strategy on EUR/USD because cost structure is most forgiving. Only branch out to other pairs once edge is verified. Use EUR/USD as the benchmark for spread, slippage and overnight-gap profile when evaluating broker quality.
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