Break-even probability
Break-even probability is the win rate at which a given price produces neither profit nor loss over the long run.
In plain English
It is identical arithmetic to implied probability, framed as a target rather than a description. If a price implies 55 percent, you need to win more than 55 percent of such bets to come out ahead.
Example
At -120 the break-even rate is about 54.5 percent. Winning exactly that leaves you flat before any other costs.
Why it matters
It converts a price into a pass or fail test you can apply to your own opinion, which is more useful than a vague sense that a price looks short.