As others have pointed out, both Uber and Lyft do have services where you literally share a car with another customer. These services are used by many people.

As others have pointed out, both Uber and Lyft do have services where you literally share a car with another customer. These services are used by many people. In addition, "ride sharing" also refers to the transportation itself as a shared resource, in the same way as a taxi, or even public transportation. With a system of shared transportation, not everyone needs their own vehicle which has significant financial/economic and environmental implications. tl;dr: Uber/Lyft are shared resources among people who may or may not actually be in the car together at the same time—and the resource they are sharing is transportation ("rides").