Glossary

Short definitions of terms you'll see across our election and policy-market coverage.

Implied probability: The probability a market price implies. A contract trading at $0.42 implies a 42% probability.
Binary market: A market with two outcomes (YES/NO or A/B), each priced between $0 and $1 that sum to $1.
Categorical market: A market with three or more mutually exclusive outcomes (e.g., "Who wins the 2028 primary?" with a field of candidates). All prices sum to roughly $1.
Cook PVI: Partisan Voter Index, published by Cook Political Report. Measures how a district or state voted relative to the national average in the last two presidential elections.
Swing state: A state where the presidential outcome is routinely competitive — most recently Pennsylvania, Michigan, Wisconsin, Arizona, Nevada, Georgia, North Carolina.
Electoral college: The US system that assigns 538 electoral votes across states. A candidate needs 270 to win the presidency.
Open seat: A race where no incumbent is running. Open seats are disproportionately competitive.
Incumbency advantage: The polling and fundraising boost incumbents typically receive. Shrinking but still material in most races.
Resolution source: The authoritative record a prediction market uses to settle (e.g., AP call, Federal Register notice, court filing).
Liquidity: How much volume sits on the order book. High liquidity means the market absorbs large trades without moving price; low liquidity means the displayed price is noisy.
Volume: Total value of trades ever executed in a market. Useful as a proxy for how seriously traders are pricing the outcome.
Calibration: Whether a market that prices events at X% is actually right about X% of the time. Polymarket and Kalshi both have calibration studies published.
Wisdom-of-crowds: The principle that aggregating many independent forecasts tends to outperform any single expert forecast on average.
CFTC: Commodity Futures Trading Commission — the US regulator that oversees event-contract exchanges like Kalshi.