A service road is a road running parallel to a faster, or busier road, which provides access to private properties, shops, industry, or farms (depending on the location.
They should be designed to have limited access points, so that motor traffic using the service street is only accessing the properties along it, rather than using it as an alternative to the parallel main road.
Service roads can (and should) be used as cycling infrastructure, forming continuous parallel routes alongside faster or busier roads, shared only with very low motor traffic levels.