What is the difference of an engine air filter and the cabin air filter for a 2007 Subaru outback?

The engine air filter is located above the engine and filters the incoming combustion air for the engine. These should be checked every oil change and depending on where and how you drive they should be replaced about every other to every third oil change or else bad gas mileage and poor engine performace will occur.

The cabin air filter removes dust and pollen from the air entering the interior of the car through the heating and air conditioning system when the control is set to "fresh air" or "outside air". This is less critical but will eventually be clogged and will need changing.

Also normally they are different styles of air filter so a different type for each one, your owners manual should tell you the types.