Broker or dealer. Per the interwebs, a broker acts on behalf of another party, vs a dealer trades for themselves.

As distinguished from an exchange, where the exchange intermediates and becomes a middle party "simultaneously" to both sides.

The market dynamics are pretty different between broker dealers and exchanges. For instance a /ticker/ as a concept makes sense only with an exchange.

The exchanges basically pick up only the contracts or goods with the most volume and standardized & predictable goods.

To trade more exotic or niche things basically you have to find your own counterparty, versus the exchange acts as an "typical" buyer and seller to each side (assuming there is anyone there at all to participate on each side... giving rise to the concept of market makers who undertake to do just that, i.e., to be ready to trade either side at any time in a certain good).