Leverage
Leverage is expressed as a ratio — 10:1 means a trader controls $10 of market exposure for every $1 of their own money. The appeal is that gains on the full $10 position accrue to the trader, not just gains on the $1 deposit. That same mathematics, however, applies equally to losses, which is why leverage is described as a tool that cuts in both directions.
Suppose a trader deposits $1,000 and uses 5:1 leverage to open a $5,000 position in a currency pair. A 5% rise in the asset produces a $250 gain — a 25% return on the $1,000 deposited. A 5% fall produces a $250 loss, wiping out a quarter of the deposit just as quickly. Higher leverage compresses the price move needed to eliminate the entire deposit to near zero.
Leverage shows up across commodities, crypto, forex, and stocks markets in different forms: futures contracts are inherently leveraged, margin accounts in equities typically offer more modest ratios, and crypto platforms have historically offered very high multiples. Economists and regulators watch aggregate leverage in a market as a measure of systemic fragility — heavily leveraged markets can unwind rapidly when prices move against the crowd. See also how futures contracts embed leverage.