Vexillology is a noun that refers to the study of flags. 

Dating back to the 1950s, the latin word vexillum (vecks ee LOOM) means ‘flag.’ By adding the suffix L-O-G-Y, which means ‘study of,’ we get our word of the day. 

As a kid, I was always a fan of cars, but as I’ve gotten older, I’d say I’ve leaned more toward vexillology as a hobby, if only because flags are a lot less expensive to collect than cars.