Suborbital pods are part of a launch system which propels a pod in a ballistic arc to the edge of space, whereupon it plummets back toward the ground, maneuvering to a new destination. These are generally used to travel very quickly between destinations on a planet when at least one of them does not possess a spaceport.
A suborbital pod station will usually actually be outside the spaceport and in the nearby city. Upon finding it, type TRANSPORT to order a pod flight. When the pod arrives, you will board automatically and be taken to your destination.
Fun facts: The first manned suborbital flight happened in 1961 and was flown by astronaut Alan Shepard. The flight took 15 minutes. Also in the real world, suborbital transport systems are being considered by several private companies, and would reduce travel times between any two destinations on Earth to under an hour.
