It is often used to describe someone who is naive, gullible, or easily taken advantage of.
The term is thought to have originated in the 18th century, referring to new immigrants to America who were often unskilled and had to work as farm laborers. These laborers were often seen as inexperienced and easy to exploit, hence the association with the color "green."
Here are some examples of how "greenhorn" can be used:
* "The new intern was a real greenhorn, asking the most basic questions."
* "Don't try to pull a fast one on me, I'm not a greenhorn anymore."
* "He was a greenhorn in the city, easily fooled by scams and con artists."