Stockmarket Terms: Fat Finger

A “Fat Finger” is?

A human error in entering a trade
A typo (extra zero, wrong price, wrong side)
What results in a large, unintended order

In simple terms:

You meant to buy $100 shares
You entered $10,000 by mistake
Suddenly, you’ve placed a trade you never intended

That single mistake can:

Move the market
Trigger algorithms
Cause a cascade of trades

Where does the term come from?

The idea of someone with “fat fingers” hitting the wrong keys on a keyboard. It’s a bit tongue-in-cheek, but it stuck because:

Trading used to be highly manual
Speed + pressure = mistakes

When did it start being used?

Originates from trading floors and early electronic trading systems

Became more prominent with:

Keyboard-based trading
Electronic order entry (1980s–2000s)

What’s happening?

A fat finger error can escalate quickly because of market structure.

1. Immediate execution

Orders hit the market instantly
No time to “take it back”

Liquidity impact

Large incorrect orders:

Sweep through order books
Move price aggressively

Algorithmic amplification

Other systems react:

Momentum algos
Market makers adjusting spreads

Cascade effects

Stop-losses triggered
Margin calls triggered
Volatility spikes

Controls and protections

Modern markets have built safeguards:

Order size limits
Price collars / circuit breakers
Pre-trade risk checks
Kill switches

The balanced takeaway

“Markets move fast, but mistakes move faster.”

For traders:

Double-check orders
Use limits and controls
Avoid rushing under pressure

Stockmarket Terms

Here is a collection of stock market terms, some you may already be familiar with, and others you may not have encountered before. Discover what they mean, explore their origins, and understand how they apply to what is happening in the market today.