If you have moved a kitchen between states, you will have heard the same piece of equipment called two different things. A grease trap and a grease arrestor do the same job: they hold back the fats, oils and grease from a commercial kitchen so they do not reach the sewer.
The difference is mostly language and scale. Grease trap is the common term on the east coast and in South Australia, and often describes the smaller under bench and near bench units. Grease arrestor is the standard term in Western Australia, and tends to describe the larger in ground units and interceptors.
In practice the servicing is the same. The unit is pumped out, the solids and fat cap removed, the chamber scraped and rinsed, the baffles checked and the waste taken away for licensed disposal. Whether the docket says trap or arrestor, the work and the trade waste obligation behind it are the same.
What does change by state is who administers your trade waste and how often you must service the unit. That is set by your local water authority, not by the name on the lid.
Wherever you are, enter your postcode and Grease Traps Australia matches you with a local operator who services traps and arrestors, at their own fixed price.