A light-hour (also written light hour) is a unit of length. It is the distance travelled by light in vacuum in one hour. Based on the current definition of the metre a light-hour is equal to 1,079,252,848,800 metres (~1.08 Tm).
This distance can easily be related to the speed of light in kilometres per hour, since light travels 1,079,252,848,800 m every hour, or 1,079,252,848.8 km/h.
To give an example, the semi-major axis of Pluto's orbit's is about 5.473 light-hours.