What does "streamline" mean?

Streamline: Of or pert. to a stream line; designating a motion or flow that is free from turbulence, like that of a particle in a streamline; hence, designating a surface, body, etc., that is designed so as to afford an unbroken flow of a fluid about it, esp. when the resistance to flow is the least possible; as, a streamline body for an automobile or airship.