加速 (jiā sù) literally means 'add speed' — the character 加 (jiā) means 'to add' or 'to increase', and 速 (sù) means 'speed' or 'velocity'. Together, they form a verb meaning 'to accelerate' — that is, to increase speed or rate of motion, development, or change. It’s commonly used in both physical contexts (e.g., vehicles speeding up) and abstract ones (e.g., accelerating economic growth or learning progress).

The word functions as a transitive verb and often appears with objects (e.g., 加速进程 — 'accelerate the process') or in compound structures like 加速器 (a particle accelerator) or 减速 (its antonym, 'to decelerate'). It’s neutral in register — appropriate in formal reports, news, technical writing, and everyday speech when discussing pace or momentum.