速率 (sù lǜ) is a noun meaning 'rate' or 'velocity' — specifically, the magnitude of how fast something changes or moves over time, without direction. It combines 速 (sù), meaning 'speed' or 'swiftness', and 率 (lǜ), meaning 'ratio', 'rate', or 'frequency'. Unlike 速度 (sù dù), which can imply directional motion (i.e., velocity as a vector), 速率 emphasizes scalar quantity — for example, '60 km/h' regardless of direction. It's commonly used in scientific, technical, and mathematical contexts, such as physics, computing (data transmission rate), and engineering.

This term appears frequently in formal writing and education, especially when distinguishing magnitude from direction. While it’s occasionally used in daily speech (e.g., internet connection speed), it sounds more precise and academic than colloquial alternatives like 速度. Learners should note that 率 here is pronounced lǜ (not shuài), matching its meaning of 'ratio' — a common pronunciation pitfall.