A "cager" is someone who is driving a 4-wheeled (or more) vehicle........a car/truck/van...whatever. The term refers to how the body of the vehicle fully encloses the occupants, thereby acting as a cage. Generally the term is used in a somewhat derogatory sense, as a way for us (motorcycle riders) to seperate ourselves from them (cagers). So, when you read a post about someone having a bad encounter with a cage, it normally means they almost got hit (or perhaps DID get hit) by a car driver. Hope this has helped
It's not a dumb question, it would've been dumb if you hadn't asked and remained confused.
Ride safe