COE stands for Certificate of Entitlement. It represents a right to vehicle ownership for 10 years.

The Vehicle Quota System (VQS) was introduced to control the vehicle population at levels supportable by road infrastructure development and planned developments in public transport and traffic management measures. The VQS sets a quota to the number of new vehicles to be registered in Singapore each year. Under the VQS, anyone who wants to register a vehicle would need to first bid for a COE through the open bidding exercises. Upon expiry of the COE, the owner would need to renew the COE for another 5 or 10 years if he wishes to keep the vehicle in Singapore beyond 10 years

Source:LTA