ATOL is air Travel Organizers Licence. A bonding scheme RUN by the Civil Aviation Authority. If your Tour operator is a member of ATOL, you are guaranteed a Refund if the company goes
into liquidation.
Other definition:
ATOL is air Travel Organiser's License. A requirement of the Civil Aviation Authority for all UK tour operators wishing to sell air seats on chartered or scheduled services. Necessitates a financial 'health check' and the putting up of a bond to cover the expense of reimbursing/repatriating tourists in the event of operator failure.