Definition - What does Omnibus Account mean?
Omnibus Account is an account used by an introducing member to execute and clear all of their customer’s trades.
Testopedia explains Omnibus Account
When an introducing broker dealer operates its business on an omnibus basis all trades are executed by the introducing broker and the clearing broker carries all of the cash and securities for the introducing broker and its customer in one omnibus account. The introducing broker must send confirmations and statements to the customers and no margin transactions are allowed. Unlike introducing broker dealers who conduct business on a fully disclosed basis the clearing member does not know who the trades are executed for or who the customers are.