middleman
A person who connects buyers and sellers in a deal.
A middleman is someone who helps connect buyers and sellers but doesn't make the product themselves. Think of a grocery store: farmers grow the food, you buy it, and the store is the middleman in between. The store buys from farmers and sells to you, making the process convenient for everyone.
Middlemen exist in many places. A talent agent is a middleman between actors and movie studios. A real estate agent is a middleman between home sellers and buyers. These middlemen know both sides of the deal and help them find each other, often earning money by taking a small percentage of the sale.
Sometimes people complain about middlemen, saying they make things more expensive. If you could buy directly from a farmer, you might pay less than at the store. But middlemen often provide real value: they gather products from many sources, handle transportation and storage, and make shopping easier. Without grocery stores as middlemen, you'd need to visit dozens of different farms just to make dinner.
The term can apply to anyone in the middle of a transaction or negotiation. If your friend asks you to pass a message to another friend instead of talking directly, you're acting as a middleman for that message.