概率 (gài lǜ) is a noun meaning 'probability' — the mathematical measure of how likely an event is to occur, expressed as a number between 0 and 1 (or 0% to 100%). The first character 概 (gài) means 'general', 'rough', or 'approximate', suggesting something not certain but estimated; the second character 率 (lǜ) means 'ratio' or 'rate', indicating a quantitative relationship. Together, they convey the idea of a 'likelihood ratio' — the proportion of favorable outcomes to all possible outcomes.

This term is widely used in mathematics, statistics, science, finance, and everyday reasoning about risk or chance. It appears in formal contexts like textbooks, news reports on polling or weather forecasts, and discussions about decision-making under uncertainty. While 概率 is standard in modern Mandarin, it’s rarely used in casual speech without context — people often say '可能性' (possibility) instead for simplicity. It’s a core technical term taught from middle school onward.