Half-giants are the result of ancient arcane tampering with humans and giants. They are very large, and unfortunately tend toward the slower end of the mental spectrum.
Due to their massive size, half-giants have two extra wound boxes in every location, and have an ED in Body. This is an exception to the rule that MDs/EDs don’t apply to Attributes; it is not an exception to the fact that only one MD or ED may be used in a single roll (so a half-giant with an ED in Fight still only rolls one on a Body + Fight roll). In hand to hand combat, half-giants can be hit with two more attacks per round than a normal-sized humanoid. Also due to their size, half-giants require double the food and water and their clothing, armor, accommodations and weapons cost double as well.
Their giant heritage also shows in the mental department. The fourth and fifth level of Knowledge and the fifth level of Charm cost double for half-giants.