A Surrogate uses her own egg to conceive the pregnancy.  A Gestational Carrier does not.  The Gestational Carrier provides a host uterus and carries a child for the Intended Parents. The surrogate provides host uterus, carries the child, and provides the egg.
Legally, using a traditional surrogate involves tremendous risk.  There can be no doubt that the surrogate is the child’s biological mother, which gives both her and her husband substantial legal footing to start from should they renege on an agreement to carry a child for others.  Some states deem traditional surrogacy agreements to be void.  Most lawyers won’t become involved with them.
Gestational carrier arrangements are much safer. Still, not all states bless them and, in fact, many have generated no law that addresses them.