A greenhorn is someone who is new to a job, activity, or situation and doesn't yet know how things work. The word suggests someone inexperienced who might make beginner mistakes simply because they haven't learned the ropes yet.

The term originally came from the American frontier, where experienced cowboys and ranchers would spot newcomers from the East who didn't know the first thing about ranch life. These greenhorns might not know how to ride a horse properly, rope cattle, or handle the challenges of the wilderness. The “green” part suggests someone fresh or unripe, like green fruit that hasn't matured yet.

Today, you might be called a greenhorn on your first day at summer camp, when you don't know where anything is or how activities work. A student starting their first day at a new school is a greenhorn until they learn the building layout and social dynamics. In any workplace, the newest employee is often the greenhorn who needs to learn procedures and systems that everyone else already knows.

The word isn't meant as an insult. It simply recognizes that everyone starts as a beginner. Even the most skilled experts were once greenhorns themselves. The key difference between a greenhorn and an experienced hand is simply time, practice, and willingness to learn from mistakes.