The bolster is the portion of a knife where the blade transitions to the handle. Besides adding strength and durability, the bolster is an integral part of the knifes balance and overall handling. When talking about kitchen knives, people will often use the terms full or semi bolster.
Full Bolster:  A bolster that extends all the way to the end of the blade and acts as a sort of finger guard.
Semi Bolster: A bolster that doesn't extend all the way to the blade, leaving the end of the blade exposed. Although this type of bolster offers less protection, it makes the knife easier to sharpen.