It seems to be the new 'it' thing – though I think it's probably been around for awhile.
When I looked up "What is Bullet Journalling?" to find out exactly, this is what I found
"The Bullet Journal is a customizable and forgiving organization system.
It can be your to-do list, sketchbook, notebook, and diary, but most likely, it will be all of the above.
It will teach you to do more with less. Get Started"