A single person, one usage space craft which can carry a spy nearly undetected to a planet.
A spy pod is a single-use one-way craft.
You need an Espionage Ministry to build a spy pod.
Some of the advantages of the spy pod over the ships capable of carrying multiple spies is the spy pod has a greater stealth rating allowing it to slip into places where a Spy Shuttle or a Dory might not be able to. Also it's cheaper and fast to build.
The Spy Pod is also a requirement of the Mercenary Guild to be able to post Mercenaries for sale.