Broker
The short answer
Someone who arranges for other people's waste to be moved or treated without ever handling it themselves. Brokers have to be registered with the regulator, the same as carriers.
In practice
The distinction that matters on paperwork is that a broker arranges the transaction while a dealer buys and sells the waste. Either way the waste itself goes straight from the producer to whoever is carrying it, and the duty of care still follows the material rather than the deal.