Greyhounds (also known as couriers or packets), are relatively small space vessels.
Greyhounds are used for the rapid transport of very high value individuals and materials.
The passenger accommodation of a greyhound, if any, is very basic and passengers are typically transported in nanostasis. Most of the ship is taken up by the drive, fuel and reaction mass. The purpose of the greyhound is to rapidly move objects from one place to another. For this they need powerful engines capable of relatively high accelerations. On seeing one for the first time, many people are surprised at how large a packet vessel is.
Greyhounds vary considerably. Some can carry a small party, others just one or two people and others can only carry packages smaller than a baseline human.
Some greyhounds may be piloted by a human but AI piloting is much more common. Many things that are moved by greyhound are confidential and the memory of an AI pilot is easier to erase.
Information too sensitive to be broadcast may be transported on a data cube in a greyhound.
Greyhounds may incorporate various systems to prevent their cargo being intercepted, tampered with or stolen.