Single Touch Payroll (also known as STP) is a government initiative to streamline your business reporting obligations regarding payroll.
Put simply, STP requires employers (or their registered agent) to report payments such salaries, wages, PAYG withholding, and superannuation information directly to the ATO from their payroll system. This must be reported after every pay run has been finalised by no later that the employee's payment date.
Starting July 1, 2019, all employers must be STP compliant.
Note: STP is already compulsory for employers with 20 or more employees.
You may check ATO's website for additional information.