Motorised infantry is infantry which is transported by trucks or other motor vehicles. It is distinguished from mechanized infantry, which is carried in armoured half-tracks or armoured personnel carriers.
Motorising infantry is the first stage towards the mechanisation of an army. Civilian trucks are readily adaptable to military uses of transporting soldiers, towing guns, and carrying equipment and supplies. This greatly increases the strategic mobility of infantry units, which would otherwise rely on marches or railroads.
Motorisation provides no direct tactical advantage in combat, because trucks and jeeps are vulnerable to artillery and small arms fire. For winter and mountain use, light tracked vehicles were employed, the Swedish made Snow Trac and Bv202 both found service with the British military. But it does increase the infantry's flexibility, because motorized elements can travel with their own integral support weapons (heavy machine guns, mortars and artillery, anti-tank weapons, etc.).
The disadvantages of motorisation is that the formation becomes dependent on supplies of fuel.
The speed advantages of motorised infantry first became important in WW2 in the German Blitzkrieg. While in combat effectiveness not more robust than regular infantry (which was foot infantry), its speed component became decisive in the Blitzkrieg strategy, because it could follow the panzer forces and defend its flanks.