Light infantry are a class of infantry in many Close Combat games. They are characterized by their relatively fast movement speed, light armament (usually consisting of rifles and grenades), and generally large unit size. They are considered the basic units of all factions.
Rifle infantry are the standard light infantry of the Soviet forces. They are each armed with a rifle and grenades, placing their range at medium to long. Due to their slow firing but high-damage rifles, they are less suited to frontal assaults as they are to defense and flanking. Their grenades allow them to be mildly effective against entrenched enemies as well as light armor.
The rifle half-team is just that -- a half of a rifle squad. They are armed with the same equipment as a normal rifle squad, but have reduced numbers and usually lower experience, as well as a slightly lower cost.