Prediction Market Terms: 25 Words You Need to Know

Every field has its own vocabulary, and prediction markets are no different. Whether you are brand new to Polymarket or looking to level up your understanding, mastering these 25 terms will help you trade more confidently and communicate more effectively with other participants.

Core Concepts

1. Prediction Market

An exchange where participants trade contracts based on the outcome of future events. Prices reflect the collective probability estimate of the crowd.

2. Share

A single unit of a prediction market contract. Shares are priced between $0.01 and $0.99. A correct share pays $1.00 at resolution. An incorrect share pays $0.00.

3. Yes Share / No Share

Each market has two sides. A "Yes" share profits if the event happens. A "No" share profits if it does not. Their prices always sum to approximately $1.00.

4. Resolution

The process of determining the outcome of a market. When an event occurs (or fails to occur by the deadline), the market "resolves" and payouts are distributed. Markets resolve to either Yes ($1.00 for Yes holders) or No ($1.00 for No holders).

5. Resolution Criteria

The specific, predefined rules that determine how a market resolves. These criteria define the exact conditions, the resolution source (e.g., official government data, AP call), and any edge cases. Always read these before trading.

6. Implied Probability

The probability of an event occurring as estimated by the market price. A share priced at $0.65 implies a 65% probability. This is the market's consensus forecast.

Trading Terms

7. Market Order

An order to buy or sell shares immediately at the best available price. Market orders execute instantly but may suffer from slippage in thin markets.

8. Limit Order

An order to buy or sell shares at a specific price or better. Limit orders only execute if the market reaches your specified price. They give you more control but may not fill if the market moves away from your price.

9. Bid

The highest price a buyer is willing to pay for a share. The bid represents current buying demand.

10. Ask

The lowest price a seller is willing to accept for a share. The ask represents current selling supply.

11. Spread

The difference between the bid and ask prices. A tight spread (e.g., $0.01) indicates high liquidity. A wide spread (e.g., $0.05+) indicates low liquidity and higher trading costs.

12. Slippage

The difference between the expected price of a trade and the actual price at which it executes. Slippage occurs in large orders or thin markets. Limit orders help avoid excessive slippage.

13. Position

Your current holdings in a particular market. If you own 100 Yes shares in a market, your position is "long 100 Yes." Positions can be sold at any time before resolution.

14. Long

Buying shares with the expectation that the price will rise (or the event will happen). "Going long Yes" means buying Yes shares.

15. Short

In prediction markets, shorting typically means buying No shares (betting the event will not happen). Some platforms also allow traditional short selling of Yes shares.

Market Structure Terms

16. Liquidity

The ease with which shares can be bought or sold without significantly affecting the price. High-liquidity markets have tight spreads, deep order books, and large trading volumes. Low-liquidity markets may have wide spreads and significant slippage.

17. Order Book

The list of all outstanding buy and sell orders for a market. The order book shows the depth of liquidity at each price level and helps traders understand supply and demand.

18. Volume

The total amount of money traded in a market over a given period. High volume generally indicates strong interest and better liquidity. It is one of the most useful indicators of market health.

19. Open Interest

The total number of outstanding shares in a market. High open interest means many participants have active positions, which generally supports better liquidity and more accurate pricing.

20. Market Maker

A participant who provides liquidity by placing both buy and sell orders in a market. Market makers profit from the spread between their bid and ask prices. They play a crucial role in keeping markets liquid and tradeable.

Advanced Terms

21. Arbitrage

Profiting from price differences for the same event across different platforms. If Polymarket prices an event at 60% and another platform prices it at 55%, an arbitrageur can buy on the cheaper platform and sell on the expensive one for a risk-free profit.

22. Calibration

How well a forecaster's probability estimates match actual outcomes over time. If you say "70% likely" about 100 events, roughly 70 should happen if you are well-calibrated. Markets as a whole tend to be well-calibrated; individual traders vary widely.

23. Edge

An information or analytical advantage that allows a trader to consistently identify mispriced markets. Edge can come from domain expertise, speed of information processing, better analytical models, or superior probability calibration.

24. Expected Value (EV)

The average outcome of a trade if it were repeated many times. A positive expected value trade is one where your estimated probability exceeds the market price (for Yes shares) or is below the market price (for No shares). Consistently finding +EV trades is the key to long-term profitability.

25. USDC

USD Coin, a stablecoin pegged to the US dollar. Polymarket uses USDC for all trades. One USDC is always worth approximately one US dollar, providing stability for traders.

Quick Reference Table

FAQ

Do I need to know all these terms to start trading?

No. Start with the core concepts (shares, resolution, implied probability) and learn the rest as you go. The trading terms become relevant as you move beyond basic market orders.

What is the most important term for beginners?

"Resolution criteria" is arguably the most important term. Understanding exactly how a market will be resolved prevents surprises and helps you make more informed trades.

Where can I learn more about prediction market strategy?

Start with hands-on experience. Place small trades, observe how markets behave, and gradually build your understanding of more advanced concepts like arbitrage and expected value calculation.