What is expected value (EV)?

What a stake is worth on average. Chance of winning × payout, minus what you put in.

Stake 10 on something you believe is 60% likely, with a 16 payout: on average that's 0.6 × 16 = 9.6 back, slightly negative. Believe it's 70% likely? Now it's 11.2, positive. Same market, different edge.

Expected value is the quiet voice asking: is the crowd's percent wrong, or is mine?