Both in a modern and historical sense
In: Other
Annie Jacobson was on Joe Rogan’s [podcast](https://youtu.be/5VoVIpIzj_c). She wrote a book on the subject. She gives some good info in the video.
Gather intelligence in different forms, communicate that information back to others, and sometimes try to stop the “enemy” from getting certain info, and sometimes spread false info. If you ever get the chance to visit DC, there is a spy museum you might enjoy.
Wouldn’t you like to know?
Spy has many meanings. Most common spies are people who happen to have intelligence, then they offer that information to someone who might be interested. Sometimes for money.
OP, you should check out some fiction by Le Carrè. He was a spy for a bit and his books seem realistic compared to other spy works out there.
The movies are a bit slow because it’s mainly men and women talking about plans and whatever. But the books are great and informative.
They get info. They steal documents, track troop movements, gather info on supply shipments, anything you can think of.