In the table below you can see car availability for the upcoming 7 days. You can change the period and also filter by car type or by specific cars. If a car is marked as 'Pending reservations on hold' that means that the reservation for the car is pending, and it cannot be booked again for that period at the moment. 

If a car is marked as 'Pending reservations' then the reservation is still pending, but the car can be assigned to another reservation for the same period. The system keeps cars 'on hold' to prevent duplicate reservations. 

You can set the time length when a car is kept 'on hold' through Settings menu / Rental Settings tab.