
Certified GKH Gardening Expert
I have not heard of that and an online search only brought up tiny decorative gravel in bullet shaped holders. I did find bullet edgers, but those are just concrete edgers somewhat bullet shaped.
I suspect they meant decorative rock or gravel. But any type of rock/gravel would work in your bed. Here is more information about the pros and cons of gravel as mulch.
https://www.gardeningknowhow.com/garden-how-to/design/lideas/gravel-garden-ideas.htm
https://www.gardeningknowhow.com/garden-how-to/mulch/using-river-rock-mulch-in-gardens.htm
https://www.gardeningknowhow.com/garden-how-to/mulch/crushed-stone-mulch.htm