‘天灾’ literally means ‘heaven’s calamity’ — combining 天 (tiān, ‘heaven’ or ‘sky’) and 灾 (zāi, ‘disaster’ or ‘calamity’). Historically, it reflects the traditional Chinese worldview that natural disasters originate from cosmic or heavenly forces beyond human control. Today, it refers specifically to large-scale natural disasters such as earthquakes, floods, typhoons, droughts, and volcanic eruptions — events caused by natural processes, not human action.

The term carries a formal, slightly literary tone and is commonly used in news reports, government announcements, disaster relief contexts, and academic discussions. It contrasts with 人祸 (rén huò, ‘man-made disaster’), emphasizing the non-human, uncontrollable origin of the event. While ‘act of God’ is a common English equivalent in legal and insurance contexts, ‘natural disaster’ is more widely understood and neutral in everyday usage.