means The likelihood or ratio of something happening versus not, especially as a measure of chance or risk.

from From the Old Norse oddi, meaning a point of land, an angle, or a triangle — and, by extension, an odd number, the one left over when you pair things off. That odd-one-out sense traveled into English, where it came to mean inequality and difference. By the 16th century 'odds' had drifted toward the gap between two things — the advantage or disadvantage one side holds — and from there into the gambler's mouth, where the distance between what's likely and what's not became a number you could bet on.