Nike plus is a system that consists of a sensor that goes in one shoe, an adaptor that goes onto an ipod or iphone and the nike plus website. You need to first callorbrate it so it knows how far you go with each stride. You can then listen to music while running and a virtual coach talks over the top of the music every so often to give updates on distance travelled etc. The run data is stored on the nike plus website which is also an online community for runners.