S.C. Code Ann. § 56-5-440: Through highway defined.

Every highway or portion thereof on which vehicular traffic is given preferential right-of-way, and at the entrances to which vehicular traffic from intersecting highways is required by law to yield the right-of-way to vehicles on such through highway in obedience to a stop sign, yield sign or other official traffic-control device, when such signs or devices are erected as provided in this chapter is a "through highway".