what's the differencebetween stolon and runner stem?

There is no big difference between runners and stolons. Both are modified creeping stem. Both are produced from the base of plants. Both produce adventitious roots and shoots at their nodes in order to form new plantlets. Stolons are actually arched runners which cross over small obstacles. They roughly grow vertically beneath the surface of soil. 
Example of runners: Oxalis, Cynodon, etc
Example of runners: Strawberry,Vallisneria,  etc