A rush hour (American English, British English) or peak hour (Australian English) is a part of the day during which traffic congestion on roads and crowding on public transport is at its highest. Normally, this happens twice every weekday: once in the morning and once in the afternoon or evening, the times during which the most people commute. The term is often used for a period of peak congestion that may last for more than one hour.

The term is very broad, but often refers specifically to private automobile transportation traffic, even when there is a large volume of cars on a road but not many people, or if the volume is normal but there is some disruption of speed. By analogy to vehicular traffic, the term Internet rush hour has been used to describe periods of peak data network usage, resulting in delays and slower delivery of data packets.