Guardians of the Stars
Couriers are used to transport very small cargoes as quickly as possible. They are not terribly large, but they have very large drive systems and fuel payload making up the bulk of the vessel. This allows them to reach high velocities and move quickly within systems. Their main purpose is to carry information quickly between locations in different systems. They also make good smuggling vessels, though as they don’t tend to have the ability to land on planets.
Couriers tend to have very small crews, a typical courier will run with just a pilot and a engineer. The fewer the accommodations they have the more room they have for cargo or the lower the mass that they have to move.