Translation: This is a US embassy acronym that stands for “Foreign Service National.” It’s the term for someone from the host country who works for the US Government.
(Here is something to know. FSNs very often have serious authority. Not soft power, or unofficial power, or the ability to influence someone. Real job-based power to make major decisions about your project. If you are the kind of jerk who assumes that you should focus on the American and not the FSN, I guarantee you will regret it.)