Win rate
Win rate is the share of settled bets that won, usually excluding pushes and voids.
In plain English
On its own it says little, because the price determines what win rate is needed. A 70 percent win rate on heavy favourites can lose money, and 40 percent on longer prices can be strongly profitable.
Example
Twenty wins from fifty settled bets is a 40 percent win rate, which is profitable or not depending entirely on the prices taken.
Why it matters
It is the most quoted and least informative betting statistic, and reading it without prices attached is how people are misled.