What is a cabin air filter?

Exactly that, it filters all air coming into the cabin.
All air for heating and A/C comes through this filter.

Come on Jeff do you really need to replace the cabin air filter?

This is an actual filter I removed. It was white when new.
Would you breathe through this?

Someone was breathing through this nasty filter. Its got Leaves, Dust, MOLD, who knows what is living in there.

Replace your cabin air filter
15,000 miles or 1 year.

Dirtiest Filters replaced over
1 month