Probability
Etymology
From Latin “probabilis” (credible, provable), from “probare” (to prove or test), itself from “probus” (good, honest). English used “probable” for “believable” from the 14th century; the mathematical theory arrived only after the 1654 Pascal–Fermat correspondence over a gambling problem turned chance into calculation.
noun · /prob-uh-BIL-uh-tee/
The chance that an event happens, expressed as a number between 0 (impossible) and 1 (certain).
What it names
It gives a disciplined way to reason about uncertainty instead of treating the future as either guaranteed or impossible.
Example
A 30 percent probability of rain does not mean the forecaster is wrong if it stays dry — it means dry days should outnumber wet ones roughly seven to three.
Related idea
Probability is not the same as odds: a probability of 1-in-4 (0.25) is stated as odds of 1-to-3, comparing the event against its non-occurrence rather than against all outcomes.